I published the F# unit test template and a user reports they cannot run the Visual Studio 2010 DLL with this template on Visual Studio 2012. You need to do a bindingDirect in the App.config file.
< bindingRedirect oldVersion="126.96.36.199" newVersion="188.8.131.52" />
You can find the full file content in a F# console application. The console application create the app.config by default. If this one still cannot solve your problem, you need create a runsetting file and force the legacy mode = true. Please remember to set the test run setting from Visual Studio menu: Test -> Test Settings -> Select Test Setting files... to use the runsetting you just created.
I have not found any drawback when using the Force Legacy mode. So please let me know if you found something.