After my last system restore, I got this annoying issue when I opened a VS soultion with test projects and some other project types. This is basically becasue of the "broken templates" issue. I came across this post that describes the problem and solution which in my case simply fixed running this command devenv /InstallVSTemplates from a Visual Studio command prompt with admin privs (for Vista).
In my case, that solved my problem. If you don;t have that luck then you may read all the above post and follow the rest of the steps.