Issue above was related to the fact that the proxy class on the C# side was not generated properly ..
Should be derived from
Unfortunatly the there is still an issue related to the content type of the respons sent from the server.
With the request the content type is
Content-Type: multipart/related; type="application/xop+xml"
But on the repons of this request the content type is set to :
WSE cannot support this feature !