Validate XSD Failed - The attribute is not declared

Question

I have an xsl file which has 3 skus, and then are grouped up to a product level which shows the 3 skus again:

<?xml version='1.0' encoding='UTF-8'?>  
<enfinity xsi:schemaLocation="http://www.intershop.com/xml/ns/enfinity/7.0/xcs/impex catalog.xsd http://www.intershop.com/xml/ns/enfinity/6.5/core/impex-dt dt.xsd" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.intershop.com/xml/ns/enfinity/7.0/xcs/impex" xmlns:xml="http://www.w3.org/XML/1998/namespace" xmlns:dt="http://www.intershop.com/xml/ns/enfinity/6.5/core/impex-dt" major="6" minor="1" family="enfinity" branch="enterprise" build="build">  
  <offer sku="423182110">  
    <sku>423182110</sku>  
    <short-description xml:lang="de-DE">Budlea Linen Skirt</short-description>  
    <long-description xml:lang="en-US"/>  
    <short-description xml:lang="en-US">Budlea Linen Skirt</short-description>  
    <name xml:lang="en-US">Budlea Linen Skirt</name>  
    <offered-product sku="423182110" domain="WhiteStuff-MasterRepository"/>  
    <tax-class id="Std"/>  
    <product-type name="Basic" domain="system"/>  
    <online>1</online>  
    <available>1</available>  
    <availability-status>0</availability-status>  
    <custom-attributes>  
      <custom-attribute name="sizeEU" dt:dt="string">42</custom-attribute>  
      <custom-attribute name="size_Bridge" dt:dt="string">WW STD</custom-attribute>  
      <custom-attribute name="variantCode" dt:dt="string">110</custom-attribute>  
      <custom-attribute name="colour" dt:dt="string">BANKSIDE GREEN PLAIN</custom-attribute>  
      <custom-attribute name="parentcolour" dt:dt="string" xml:lang="en-US">Green</custom-attribute>  
      <custom-attribute name="parentcolour" dt:dt="string" xml:lang="de-DE">Green</custom-attribute>  
      <custom-attribute name="Shade" dt:dt="string">None</custom-attribute>  
      <custom-attribute name="rgbColour" dt:dt="string">74AAA8</custom-attribute>  
      <custom-attribute name="size" dt:dt="string">14</custom-attribute>  
      <custom-attribute name="season" dt:dt="string">SS18</custom-attribute>  
      <custom-attribute name="story" dt:dt="string">POOLSIDE</custom-attribute>  
      <custom-attribute name="EANCode" dt:dt="string"/>  
      <custom-attribute name="bleach" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="bleach" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="dryClean" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="dryClean" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="iron" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="iron" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="temprature" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="temprature" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="tumbleDry" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="tumbleDry" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="fabric" dt:dt="string" xml:lang="en-US">Main: 100% Linen, Trim: 97% Cotton, 3% Elastane</custom-attribute>  
      <custom-attribute name="fabric" dt:dt="string" xml:lang="de-DE">Main: 100% Linen, Trim: 97% Cotton, 3% Elastane</custom-attribute>  
      <custom-attribute name="END_USE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="END_USE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="EVENT_CODE" dt:dt="string"/>  
      <custom-attribute name="LENGTH_HEIGHT" dt:dt="string" xml:lang="en-US">Below Knee </custom-attribute>  
      <custom-attribute name="LENGTH_HEIGHT" dt:dt="string" xml:lang="de-DE">Below Knee </custom-attribute>  
      <custom-attribute name="NECK_SHAPE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="NECK_SHAPE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="NEWNESS" dt:dt="string">NEW</custom-attribute>  
      <custom-attribute name="PATTERN" dt:dt="string" xml:lang="en-US">Plain</custom-attribute>  
      <custom-attribute name="PATTERN" dt:dt="string" xml:lang="de-DE">Einfarbig</custom-attribute>  
      <custom-attribute name="PATTERN_TYPE" dt:dt="string" xml:lang="en-US">Plain</custom-attribute>  
      <custom-attribute name="PATTERN_TYPE" dt:dt="string" xml:lang="de-DE">Einfarbig</custom-attribute>  
      <custom-attribute name="PRIMARY_SHAPE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="PRIMARY_SHAPE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="SLEEVE_LENGTH" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="SLEEVE_LENGTH" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="WEIGHT" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="WEIGHT" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="SHIRT_FIT" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="SHIRT_FIT" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="FABRIC_TYPE" dt:dt="string" xml:lang="en-US">Linen</custom-attribute>  
      <custom-attribute name="FABRIC_TYPE" dt:dt="string" xml:lang="de-DE">Leinen </custom-attribute>  
      <custom-attribute name="FABRIC_CONSTRUCTION" dt:dt="string" xml:lang="en-US">Woven</custom-attribute>  
      <custom-attribute name="FABRIC_CONSTRUCTION" dt:dt="string" xml:lang="de-DE">Gewoben </custom-attribute>  
      <custom-attribute name="FreightClassID" dt:dt="string">STD</custom-attribute>  
    </custom-attributes>  
  </offer>  
  <offer sku="423182111">  
    <sku>423182111</sku>  
    <short-description xml:lang="de-DE">Budlea Linen Skirt</short-description>  
    <long-description xml:lang="en-US"/>  
    <short-description xml:lang="en-US">Budlea Linen Skirt</short-description>  
    <name xml:lang="en-US">Budlea Linen Skirt</name>  
    <offered-product sku="423182111" domain="WhiteStuff-MasterRepository"/>  
    <tax-class id="Std"/>  
    <product-type name="Basic" domain="system"/>  
    <online>1</online>  
    <available>1</available>  
    <availability-status>0</availability-status>  
    <custom-attributes>  
      <custom-attribute name="sizeEU" dt:dt="string">44</custom-attribute>  
      <custom-attribute name="size_Bridge" dt:dt="string">WW STD</custom-attribute>  
      <custom-attribute name="variantCode" dt:dt="string">111</custom-attribute>  
      <custom-attribute name="colour" dt:dt="string">BANKSIDE GREEN PLAIN</custom-attribute>  
      <custom-attribute name="parentcolour" dt:dt="string" xml:lang="en-US">Green</custom-attribute>  
      <custom-attribute name="parentcolour" dt:dt="string" xml:lang="de-DE">Green</custom-attribute>  
      <custom-attribute name="Shade" dt:dt="string">None</custom-attribute>  
      <custom-attribute name="rgbColour" dt:dt="string">74AAA8</custom-attribute>  
      <custom-attribute name="size" dt:dt="string">16</custom-attribute>  
      <custom-attribute name="season" dt:dt="string">SS18</custom-attribute>  
      <custom-attribute name="story" dt:dt="string">POOLSIDE</custom-attribute>  
      <custom-attribute name="EANCode" dt:dt="string"/>  
      <custom-attribute name="bleach" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="bleach" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="dryClean" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="dryClean" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="iron" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="iron" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="temprature" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="temprature" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="tumbleDry" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="tumbleDry" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="fabric" dt:dt="string" xml:lang="en-US">Main: 100% Linen, Trim: 97% Cotton, 3% Elastane</custom-attribute>  
      <custom-attribute name="fabric" dt:dt="string" xml:lang="de-DE">Main: 100% Linen, Trim: 97% Cotton, 3% Elastane</custom-attribute>  
      <custom-attribute name="END_USE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="END_USE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="EVENT_CODE" dt:dt="string"/>  
      <custom-attribute name="LENGTH_HEIGHT" dt:dt="string" xml:lang="en-US">Below Knee </custom-attribute>  
      <custom-attribute name="LENGTH_HEIGHT" dt:dt="string" xml:lang="de-DE">Below Knee </custom-attribute>  
      <custom-attribute name="NECK_SHAPE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="NECK_SHAPE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="NEWNESS" dt:dt="string">NEW</custom-attribute>  
      <custom-attribute name="PATTERN" dt:dt="string" xml:lang="en-US">Plain</custom-attribute>  
      <custom-attribute name="PATTERN" dt:dt="string" xml:lang="de-DE">Einfarbig</custom-attribute>  
      <custom-attribute name="PATTERN_TYPE" dt:dt="string" xml:lang="en-US">Plain</custom-attribute>  
      <custom-attribute name="PATTERN_TYPE" dt:dt="string" xml:lang="de-DE">Einfarbig</custom-attribute>  
      <custom-attribute name="PRIMARY_SHAPE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="PRIMARY_SHAPE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="SLEEVE_LENGTH" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="SLEEVE_LENGTH" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="WEIGHT" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="WEIGHT" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="SHIRT_FIT" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="SHIRT_FIT" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="FABRIC_TYPE" dt:dt="string" xml:lang="en-US">Linen</custom-attribute>  
      <custom-attribute name="FABRIC_TYPE" dt:dt="string" xml:lang="de-DE">Leinen </custom-attribute>  
      <custom-attribute name="FABRIC_CONSTRUCTION" dt:dt="string" xml:lang="en-US">Woven</custom-attribute>  
      <custom-attribute name="FABRIC_CONSTRUCTION" dt:dt="string" xml:lang="de-DE">Gewoben </custom-attribute>  
      <custom-attribute name="FreightClassID" dt:dt="string">STD</custom-attribute>  
    </custom-attributes>  
  </offer>  
  <offer sku="423182112">  
    <sku>423182112</sku>  
    <short-description xml:lang="de-DE">Budlea Linen Skirt</short-description>  
    <long-description xml:lang="en-US"/>  
    <short-description xml:lang="en-US">Budlea Linen Skirt</short-description>  
    <name xml:lang="en-US">Budlea Linen Skirt</name>  
    <offered-product sku="423182112" domain="WhiteStuff-MasterRepository"/>  
    <tax-class id="Std"/>  
    <product-type name="Basic" domain="system"/>  
    <online>1</online>  
    <available>1</available>  
    <availability-status>0</availability-status>  
    <custom-attributes>  
      <custom-attribute name="sizeEU" dt:dt="string">46</custom-attribute>  
      <custom-attribute name="size_Bridge" dt:dt="string">WW STD</custom-attribute>  
      <custom-attribute name="variantCode" dt:dt="string">112</custom-attribute>  
      <custom-attribute name="colour" dt:dt="string">BANKSIDE GREEN PLAIN</custom-attribute>  
      <custom-attribute name="parentcolour" dt:dt="string" xml:lang="en-US">Green</custom-attribute>  
      <custom-attribute name="parentcolour" dt:dt="string" xml:lang="de-DE">Green</custom-attribute>  
      <custom-attribute name="Shade" dt:dt="string">None</custom-attribute>  
      <custom-attribute name="rgbColour" dt:dt="string">74AAA8</custom-attribute>  
      <custom-attribute name="size" dt:dt="string">18</custom-attribute>  
      <custom-attribute name="season" dt:dt="string">SS18</custom-attribute>  
      <custom-attribute name="story" dt:dt="string">POOLSIDE</custom-attribute>  
      <custom-attribute name="EANCode" dt:dt="string"/>  
      <custom-attribute name="bleach" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="bleach" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="dryClean" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="dryClean" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="iron" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="iron" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="temprature" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="temprature" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="tumbleDry" dt:dt="boolEANCode" xml:lang="en-US"/>  
      <custom-attribute name="tumbleDry" dt:dt="boolEANCode" xml:lang="de-DE"/>  
      <custom-attribute name="fabric" dt:dt="string" xml:lang="en-US">Main: 100% Linen, Trim: 97% Cotton, 3% Elastane</custom-attribute>  
      <custom-attribute name="fabric" dt:dt="string" xml:lang="de-DE">Main: 100% Linen, Trim: 97% Cotton, 3% Elastane</custom-attribute>  
      <custom-attribute name="END_USE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="END_USE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="EVENT_CODE" dt:dt="string"/>  
      <custom-attribute name="LENGTH_HEIGHT" dt:dt="string" xml:lang="en-US">Below Knee </custom-attribute>  
      <custom-attribute name="LENGTH_HEIGHT" dt:dt="string" xml:lang="de-DE">Below Knee </custom-attribute>  
      <custom-attribute name="NECK_SHAPE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="NECK_SHAPE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="NEWNESS" dt:dt="string">NEW</custom-attribute>  
      <custom-attribute name="PATTERN" dt:dt="string" xml:lang="en-US">Plain</custom-attribute>  
      <custom-attribute name="PATTERN" dt:dt="string" xml:lang="de-DE">Einfarbig</custom-attribute>  
      <custom-attribute name="PATTERN_TYPE" dt:dt="string" xml:lang="en-US">Plain</custom-attribute>  
      <custom-attribute name="PATTERN_TYPE" dt:dt="string" xml:lang="de-DE">Einfarbig</custom-attribute>  
      <custom-attribute name="PRIMARY_SHAPE" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="PRIMARY_SHAPE" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="SLEEVE_LENGTH" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="SLEEVE_LENGTH" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="WEIGHT" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="WEIGHT" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="SHIRT_FIT" dt:dt="string" xml:lang="en-US"/>  
      <custom-attribute name="SHIRT_FIT" dt:dt="string" xml:lang="de-DE"/>  
      <custom-attribute name="FABRIC_TYPE" dt:dt="string" xml:lang="en-US">Linen</custom-attribute>  
      <custom-attribute name="FABRIC_TYPE" dt:dt="string" xml:lang="de-DE">Leinen </custom-attribute>  
      <custom-attribute name="FABRIC_CONSTRUCTION" dt:dt="string" xml:lang="en-US">Woven</custom-attribute>  
      <custom-attribute name="FABRIC_CONSTRUCTION" dt:dt="string" xml:lang="de-DE">Gewoben </custom-attribute>  
      <custom-attribute name="FreightClassID" dt:dt="string">STD</custom-attribute>  
    </custom-attributes>  
  </offer>  
  <offer sku="423182">  
    <sku>423182</sku>  
    <short-description xml:lang="de-DE">Budlea Linen Skirt</short-description>  
    <long-description xml:lang="en-US"/>  
    <short-description xml:lang="en-US">Budlea Linen Skirt</short-description>  
    <name xml:lang="en-US">Budlea Linen Skirt</name>  
    <variations>  
      <mastered-products>  
        <mastered-product sku="423182110" domain="WhiteStuff-MasterRepository" default="1" productvariationposition="500"/>  
        <mastered-product sku="423182111" domain="WhiteStuff-MasterRepository" default="0" productvariationposition="600"/>  
        <mastered-product sku="423182112" domain="WhiteStuff-MasterRepository" default="0" productvariationposition="700"/>  
      </mastered-products>  
      <variation-attributes>  
        <variation-attribute name="size">  
          <presentation-option>default</presentation-option>  
          <custom-attributes>  
            <custom-attribute name="displayName" dt:dt="string" xml:lang="en-US">Size</custom-attribute>  
          </custom-attributes>  
        </variation-attribute>  
        <variation-attribute name="colour">  
          <presentation-option>colorCode</presentation-option>  
          <presentation-product-attribute-name>rgbColour</presentation-product-attribute-name>  
          <custom-attributes>  
            <custom-attribute name="displayName" dt:dt="string" xml:lang="en-US">Colour</custom-attribute>  
          </custom-attributes>  
        </variation-attribute>  
      </variation-attributes>  
    </variations>  
    <offered-product sku="423182" domain="WhiteStuff-MasterRepository"/>  
    <tax-class id="FullTax"/>  
    <product-type name="Basic" domain="system"/>  
    <online>1</online>  
    <available>1</available>  
    <availability-status>0</availability-status>  
    <manufacturer>  
      <manufacturer-name/>  
      <manufacturer-sku/>  
    </manufacturer>  
    <custom-attributes>  
      <custom-attribute name="sizeBridge" dt:dt="string">WW STD</custom-attribute>  
      <custom-attribute name="washCareProfile" dt:dt="string">Machine Washable</custom-attribute>  
    </custom-attributes>  
  </offer>  
</enfinity>   

I used VisualStudio to create an XSD:

<?xml version="1.0" encoding="utf-8"?>  
<xs:schema xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:dt="http://www.intershop.com/xml/ns/enfinity/6.5/core/impex-dt" attributeFormDefault="unqualified" elementFormDefault="qualified" targetNamespace="http://www.intershop.com/xml/ns/enfinity/7.0/xcs/impex" xmlns:xs="http://www.w3.org/2001/XMLSchema">  
    <xs:import namespace="http://www.w3.org/XML/1998/namespace" />  
    <xs:import namespace="http://www.intershop.com/xml/ns/enfinity/6.5/core/impex-dt" />  
    <xs:element name="enfinity">  
        <xs:complexType>  
            <xs:sequence>  
                <xs:element maxOccurs="unbounded" name="offer">  
                    <xs:complexType>  
                        <xs:sequence>  
                            <xs:choice maxOccurs="unbounded">  
                                <xs:element name="sku" type="xs:unsignedInt" />  
                                <xs:element name="short-description">  
                                    <xs:complexType>  
                                        <xs:simpleContent>  
                                            <xs:extension base="xs:string">  
                                                <xs:attribute ref="xml:lang" use="required" />  
                                            </xs:extension>  
                                        </xs:simpleContent>  
                                    </xs:complexType>  
                                </xs:element>  
                                <xs:element name="long-description">  
                                    <xs:complexType>  
                                        <xs:attribute ref="xml:lang" use="required" />  
                                    </xs:complexType>  
                                </xs:element>  
                                <xs:element name="name">  
                                    <xs:complexType>  
                                        <xs:simpleContent>  
                                            <xs:extension base="xs:string">  
                                                <xs:attribute ref="xml:lang" use="required" />  
                                            </xs:extension>  
                                        </xs:simpleContent>  
                                    </xs:complexType>  
                                </xs:element>  
                                <xs:element name="offered-product">  
                                    <xs:complexType>  
                                        <xs:attribute name="sku" type="xs:unsignedInt" use="required" />  
                                        <xs:attribute name="domain" type="xs:string" use="required" />  
                                    </xs:complexType>  
                                </xs:element>  
                                <xs:element name="tax-class">  
                                    <xs:complexType>  
                                        <xs:attribute name="id" type="xs:string" use="required" />  
                                    </xs:complexType>  
                                </xs:element>  
                                <xs:element name="product-type">  
                                    <xs:complexType>  
                                        <xs:attribute name="name" type="xs:string" use="required" />  
                                        <xs:attribute name="domain" type="xs:string" use="required" />  
                                    </xs:complexType>  
                                </xs:element>  
                                <xs:element name="online" type="xs:unsignedByte" />  
                                <xs:element name="available" type="xs:unsignedByte" />  
                                <xs:element name="availability-status" type="xs:unsignedByte" />  
                                <xs:element name="custom-attributes">  
                                    <xs:complexType>  
                                        <xs:sequence>  
                                            <xs:element maxOccurs="unbounded" name="custom-attribute">  
                                                <xs:complexType>  
                                                    <xs:simpleContent>  
                                                        <xs:extension base="xs:string">  
                                                            <xs:attribute name="name" type="xs:string" use="required" />  
                                                            <xs:attribute ref="dt:dt" use="required" />  
                                                            <xs:attribute ref="xml:lang" use="optional" />  
                                                        </xs:extension>  
                                                    </xs:simpleContent>  
                                                </xs:complexType>  
                                            </xs:element>  
                                        </xs:sequence>  
                                    </xs:complexType>  
                                </xs:element>  
                                <xs:element name="variations">  
                                    <xs:complexType>  
                                        <xs:sequence>  
                                            <xs:element name="mastered-products">  
                                                <xs:complexType>  
                                                    <xs:sequence>  
                                                        <xs:element maxOccurs="unbounded" name="mastered-product">  
                                                            <xs:complexType>  
                                                                <xs:attribute name="sku" type="xs:unsignedInt" use="required" />  
                                                                <xs:attribute name="domain" type="xs:string" use="required" />  
                                                                <xs:attribute name="default" type="xs:unsignedByte" use="required" />  
                                                                <xs:attribute name="productvariationposition" type="xs:unsignedShort" use="required" />  
                                                            </xs:complexType>  
                                                        </xs:element>  
                                                    </xs:sequence>  
                                                </xs:complexType>  
                                            </xs:element>  
                                            <xs:element name="variation-attributes">  
                                                <xs:complexType>  
                                                    <xs:sequence>  
                                                        <xs:element maxOccurs="unbounded" name="variation-attribute">  
                                                            <xs:complexType>  
                                                                <xs:sequence>  
                                                                    <xs:element name="presentation-option" type="xs:string" />  
                                                                    <xs:element minOccurs="0" name="presentation-product-attribute-name" type="xs:string" />  
                                                                    <xs:element name="custom-attributes">  
                                                                        <xs:complexType>  
                                                                            <xs:sequence>  
                                                                                <xs:element name="custom-attribute">  
                                                                                    <xs:complexType>  
                                                                                        <xs:simpleContent>  
                                                                                            <xs:extension base="xs:string">  
                                                                                                <xs:attribute name="name" type="xs:string" use="required" />  
                                                                                                <xs:attribute ref="dt:dt" use="required" />  
                                                                                                <xs:attribute ref="xml:lang" use="required" />  
                                                                                            </xs:extension>  
                                                                                        </xs:simpleContent>  
                                                                                    </xs:complexType>  
                                                                                </xs:element>  
                                                                            </xs:sequence>  
                                                                        </xs:complexType>  
                                                                    </xs:element>  
                                                                </xs:sequence>  
                                                                <xs:attribute name="name" type="xs:string" use="required" />  
                                                            </xs:complexType>  
                                                        </xs:element>  
                                                    </xs:sequence>  
                                                </xs:complexType>  
                                            </xs:element>  
                                        </xs:sequence>  
                                    </xs:complexType>  
                                </xs:element>  
                                <xs:element name="manufacturer">  
                                    <xs:complexType>  
                                        <xs:sequence>  
                                            <xs:element name="manufacturer-name" />  
                                            <xs:element name="manufacturer-sku" />  
                                        </xs:sequence>  
                                    </xs:complexType>  
                                </xs:element>  
                            </xs:choice>  
                        </xs:sequence>  
                        <xs:attribute name="sku" type="xs:unsignedInt" use="required" />  
                    </xs:complexType>  
                </xs:element>  
            </xs:sequence>  
            <xs:attribute name="major" type="xs:unsignedByte" use="required" />  
            <xs:attribute name="minor" type="xs:unsignedByte" use="required" />  
            <xs:attribute name="family" type="xs:string" use="required" />  
            <xs:attribute name="branch" type="xs:string" use="required" />  
            <xs:attribute name="build" type="xs:string" use="required" />  
        </xs:complexType>  
    </xs:element>  
</xs:schema>  

But when I tried to open it in Visual Studio I get this error: This schema is an invalid XSD Schema and has the following error(s):

The 'http://www.intershop.com/xml/ns/enfinity/6.5/core/impex-dt:dt' attribute is not declared.
The 'http://www.intershop.com/xml/ns/enfinity/6.5/core/impex-dt:dt' attribute is not declared.
I can see a bunch of dt:dt in the xml file, which I think means it's referencing other elements, but how do I modified my XSD schema file so I can at least open it in Visual Studio without errors and validate it?