I have encountered an exception when I use Entity Framework 4.0 RC. My Entity Framework model is encapsulated in a private assembly who\'s name is Procurement.EFDataProvider
In my case it was essentialy the same issue, the mapping not being exactly as expected. What happened to me was that I had move a property in a "Table Per Hierarchy inheritance" from one of the subclasses to the base class and forgot to update the model.
I have custom POCO and by copying the edmx file to a blank new project and let it autogenerate the entities, then compare them to what I had helped me in finding the difference.