Visual Studio test executor no longer attempts to run tests for assemblies that appear to not be Fixie test assemblies, just like the Visual Studio test discoverer.  Although this would rarely matter, problems would surface when an instance of VS remains open, but a Fixie based solution is closed and a non-Fixie based solution is opened in the same Visual Studio instance.  Fixie's runner would still be loaded by VS, and can be invoked incorrectly, resulting in failures when Fixie.dll cannot be found.