We are using Visual Studio 2012 and Team Foundation Server 2010 in our project. Since, we are using Microsoft Fakes, we could have not used the started Test functionality of
I had the same error message just now with Visual Studio 2017 using the new MSTest.Framework and MSTest.TestAdapter (to be able to use Live Unit Testing). It turned out I was using multiple versions of those packages in my solution. Consolidating them to the latest version solved the problem.