Error mocking an interface

Okay, my first line of code ever is giving me an error:

Isolate.Fake.Instance<ILoginScreen>(Members.MustSpecifyReturnValues);

Results in:

System.TypeLoadException: Type 'Mock0000ILoginScreen' from assembly 'DynamicMockAssembly, Version=0.0.0.0, Culture=neutral, PublicKeyToken=a0857b23fb3f20d9' is attempting to implement an inaccessible interface..

The interface is marked as "internal" in the DLL I'm unit testing. I've used the [InternalsVisibleTo] to make it accessible to the test DLL. I can work around this by adding:

[assembly: InternalsVisibleTo("DynamicMockAssembly")]

But I figured mocking internals was no sweat for TypeMock.