Adding tags to a Header with AddressHeader.CreateAddressHeader

Question

I am trying to add some tags to the Header of a SOAP request, but I cannot insert this tag:
<ReplyTo xmlns="http://www.w3.org/2005/08/addressing">
<Address>http://www.w3.org/2005/08/addressing/anonymous</Address>
</ReplyTo>

I tried to insert it like this:

string cValue = "<Address>http://www.w3.org/2005/08/addressing/anonymous</Address>";
   AddressHeader oReplyTo = AddressHeader.CreateAddressHeader("ReplyTo",
                                                              "http://www.w3.org/2005/08/addressing",
                                                              cValue);

But I got this result:

<ReplyTo xmlns="http://www.w3.org/2005/08/addressing">&lt;Address&gt;http://www.w3.org/2005/08/addressing/anonymous&lt;/Address&gt;</ReplyTo>

How can I do it correctly? Is there any other way besides AddressHeader.CreateAddressHeader?

Thanks for your help.