Could not load file or assembly TypeMock.Interceptors

We have just upgraded Typemock from 6.0.2.0 to Typemock 7.3.0.0. And we now get the following error at runtime:

[System.IO.FileNotFoundException] = {"Could not load file or assembly 'TypeMock.Interceptors, Version=0.0.0.0, Culture=neutral, PublicKeyToken=0000000000000000' or one of its dependencies. The system cannot find the file specified.":"TypeMock.Interceptors, Version=0.0.0.0, Culture=neutral, Pu...

During debugging I can see that the source throwing it is mscorlib. The mystifying thing is that I have unloaded all of my projects that have references to Typemock.dlls but still get this error. When I choose "suspend mocking" in the Typemock-menu everything works.

In the GAC I can see that Typemock.Interceptors 7.3.0.0 is installed.

Any ideas?