I remember spending one or two days trying to sort out this issue. It was quite annoying, mainly because the hardest part was already developed in Visual Studio 2012, and I couldn’t see the content type from my BCS connexion.
Go to “Central Administration->Manage Service Applications->Business Data Connectivity Service”. Be sure you BDC Connexion is there. If it is, select it, and go to “Set Object Permissions” and set “All Authenticated Users” enable for Edit, Execute, Selectable In Clients and Set Permissions. Tick “Propagate permissions to all methods of this external content type. Doing so will overwrite existing permissions.”.
After doing this, everything should work an look like this:
If you still having the same problem… be sure when you go to your “BDC Explorer” under Visual Studio 2012, select TypeDescriptor and the “Identifier” is select it. That is the main link between the class and the entity. For example here, I select BaseUri TypeDescriptor and I link it with BaseUri from the class.
There are more problems related. but I think this is a good start point.