An "AssemblyName context property was not valid" error occurs when submitting a document to a Web service via an orchestration

Problem

Submitting a document to a Web service via an orchestration results in an "AssemblyName context property not valid" error.

Cause

The BizTalk application was originally designed using a "messaging" approach without an intervening orchestration. This type of solution uses a send port filter to link the receive port and the send port so that the document is passed through to the send port upon receipt. Later, the solution was modified to include an orchestration that was bound to the send port.

Resolution

Remove the filter on the send port. If you apply a filter to a send port that is bound to an orchestration, messages will often bypass the orchestration and cause the context property error.

Source: Microsoft