The EntityContainer name must be unique. An EntityContainer with the name 'Entities' is already defined

Question

For a little background:

I have a DLL project with the following structure:

Rivworks.Model (project)  
  \\Negotiation (folder)  
      Model.edmx          


        

Answer 1

Your two EDMX files probably have the same entity container name. You need to change (at least) one of them.

In the GUI designer, open Model Browser. Look for a node that says "EntityContainer: Entities". Click it. In Properties, change Name to something else. Save and rebuild.