Hi,
The examples I’ve come across on the internet all use a strongly typed message in the Receive location for the orchestration when it is exposed as a WCF service. So the publishing wizard exposes your untyped message as of type Object. In your project that tests the service, have you tried constructing a message of type XmlDocument, cast it as an Object and pass that to the service proxy call? I’m not sure if that would work, but give it a try.
If this does not work, you would have to re-architect your orchestration to use a proper schema for your Receive location.
Daniel.