I’m working on a new Visual Studio addin that launches a profiling application that in turn runs unit and load tests. I can’t recall how I created the project, but it must not have been by using the addin wizard. When I debugged the addin in another instance of Visual Studio, I got an error indicating that the addin couldn’t be loaded or threw an exception. The additional information it gave was "No such interface supported".
After pulling my hair out for quite a while, the answer was that the AssemblyInfo.cs contained the following: