BizTalk - AssemblyName context property was not valid

I've been working in BizTalk Server 2004 for a while now, so I'm going to be publishing some of the most difficult BizTalk problems I have solved...

Here is one particular error
AssemblyName context property was not valid
or
Microsoft.XLANGs.Core.XlangSoapException: An error occurred while processing
the message, refer to the details section for more information
at Microsoft.BizTalk.XLANGs.BTXEngine.BTXPortBase.VerifyTransport(Envelope env, Int32 operationId, Context ctx) at
Microsoft.XLANGs.Core.Subscription.Receive(Segment s, Context ctx, Envelope&
env, Boolean topOnly) at Microsoft.XLANGs.Core.PortBase.GetMessageId(Subscription subscription, Segment currentSegment, Context cxt, Envelope& env, CachedObject
location) at SCE_FlatFileTest.SCE_flatfile.segment1(StopConditions stopOn)
at Microsoft.XLANGs.Core.SegmentScheduler.RunASegment(Segment s, StopConditions stopCond, Exception& exp)Microsoft.XLANGs.Core.XlangSoapExceptionScoped@SCE_flatfile.SCE_flatfile2dfdb796-dafc-4e08-af1d-683128013b6f

This happened in one of Orchestrations that was trying to submit a request/response message to a web service. I added the web reference already and all schemas matched correctly. What was going on?

Well, the port I specified for the web service had the wrong port type. When I created the port I elected to create a NEW port type instead of selecting an existing one - the one that is automatically created when you add a web service. Doh!!!

Once I made that change, the above errors went away.