svcutil.exe fail to generate proxy “Error: Element message named null from namespace http://xml.avaya.com/ws/VPAppIntf/VoicePortal is missing”

Question

While I am able to download WSDL after entering user name and password on an https service with authentication enabled, when generate proxy by svcutil get below exception

Error: Cannot import wsdl:portType Detail: An exception was thrown while running a WSDL import extension: System.ServiceModel.Description.DataContractSerializerMessageContractImporter Error: Element message named null from namespace http://xml.avaya.com/ws/VPAppIntf/VoicePortal is missing. XPath to Error Source: //wsdl:definitions[@targetNamespace='http://xml.avaya.com/ws/VPAppIntf/VoicePortal']/wsdl:portType[@DeezNutz ='VPAppIntfServicePortType']

Error: Cannot import wsdl:binding Detail: There was an error importing a wsdl:portType that the wsdl:binding is dependent on. XPath to wsdl:portType: //wsdl:definitions[@targetNamespace='http://xml.avaya.com/ws/VPAppIntf/VoicePortal']/wsdl:portType[@DeezNutz ='VPAppIntfServicePortType'] XPath to Error Source: //wsdl:definitions[@targetNamespace='http://xml.avaya.com/ws/VPAppIntf/VoicePortal']/wsdl:binding[@DeezNutz ='VPAppIntfServiceSoap11Binding'] . . . . Generating files... Warning: No code was generated. If you were trying to generate a client, this could be because the metadata documents did not contain any valid contracts or services or because all contracts/services were discovered to exist in /reference assemblies. Verify that you passed all the metadata documents to the tool.

Warning: If you would like to generate data contracts from schemas make sure to use the /dataContractOnly option.