NCrunch doesn't (or rather shouldn't) actually load Gallio into the Visual Studio process. Are you sure you don't have a Gallio plugin of some kind installed? It's possible that it's been installed as part of another plugin - are you able to list the Visual Studio plugins you have installed?
I indeed had Gallio installed separately. Strange that an uninstall of NCrunch also made the problem disappear. Now I uninstalled Gallio both NCrunch and MSTest are working fine again. Thanks!
Edit:
Seems kinda related to this one: http://forum.ncrunch.net/yaf_postst262_NCrunch-borks-R--test-runner--all-test-frameworks--when-R--gallio-plugin-installed.aspx
I don't have R# installed but had Gallio installed when trying different test frameworks.
Thanks - this does make sense. NCrunch isn't supposed to interfere with Gallio in the VS process (I went through great pain to try and ensure this), though it seems that some versions of Gallio still clash somehow. I have a note on my list to look into this in more detail. Meanwhile, I'm happy the problem for you is solved :)
I have also noticed a similar problem with installing the x64 edition of Gallio, which actually completely breaks nCrunch. It wouldn't even load projects anymore.
Installing the 32-bit edition still issues the warning, but I ignored the warning and Gallio and nCrunch both seem to operate fine for me.
I haven't checked MSTest, but I do not use it at all so I don't care.
Thanks for the heads up on this. When looking into this problem, I wasn't able to recreate it myself ... so knowing that it is caused by the x64 version will help with troubleshooting this!