Assembler cannot retrieve document specification by using this type

This error message can mean one of two things:

1. You don't have a schema deployed with a typename that matches the instance document coming through the system.

2. You have more than one schema deployed that matches the typename. We do a lookup on typename and see two schema deployed and can't choose without user guidance which one to use.

The second condition actually happens more regularly than you would initially think. For example: If you use the webservices “add web reference“ a reference.xsd schema is added to your project and if this schema was already deployed on your system you now have two copies.

So how do you get around this issue? One option is to reduce to a single schema, but that's not always possible. Another is to go ahead and create a custom pipeline (send or receive depending on what you are trying to do). Drag in the assembler/dissasembler (eg. XML) and set the property "Document Schemas" explicitly to point to the typename you want. That way we don't do a look-up and your error magically disappears...

Another solution is to change the namespace of the reference.xsd schema...

(Source: http://blogs.msdn.com/scottwoo/archive/2004/06/07/150174.aspx)