Soap Extension - ChainStream has a null request stream

Using VS 2005 and .NET 2.0

I'm trying to adapt the code from this article http://msdn.microsoft.com/msdnmag/issues/03/03/WebServices/ and this article http://www.codeproject.com/cs/webservices/SerializationFun.asp for use on a winform client.

Winform works without the SoapExtension implementation.  But when I hook into the web reference (reference.cs) by adding an attribute [XmlStreamSoapExtension()] to the method, something is breaking the request stream and makes it null.  ChainStream is given a null stream to work with.

Any ideas what might be causing it