After a good 2 hours of searching what the **** happened and Visual Studio stopped working, I finally found a working solution..!

Just copy all dte*.olb files, from C:\Program Files (X86)\Common Files\Microsoft Shared\MSEnv to C:\Program Files X86\Microsoft Visual Studio 9.0\Common7\IDE.

Just for the record, I tried “devenv /resetuserdata” and deleting the involved registry keys with no luck at all. I end up using Process Monitor after reading this post: http://blogs.msdn.com/b/visualstudio/archive/2009/10/29/how-to-fix-the-application-cannot-start-error.aspx?PageIndex=4&WT.mc_id=DT-MVP-5004591.

With a little luck and a lot of tries, I got a headache and a working studio.