Entity Framework Duplicate type name within an assembly (6.1.0)
As a work around, this only happens if you are single-stepping using the debugger. If you place your break point a few lines further down inside your source, the error will not show up.
I haven't uninstalled, and this at least allows me to continue working.
This is a new issue with EF 6.1.0, and the EF team is aware of the problem:
Faced the same in my WCF webservice recently. Just clean your solution and rebuild it. This should fix the issue.