incompatible csproj

I built unity project to windows phone 8. When I opened the .sln file, I got error that csproj is incompatible with my current version of visual studio. I'm using vs ultimate 2012 I got from my school. I researched to microsoft forum and they said about opening the vs studio using devenv /ResetSkipPkgs, but it doesn't help me.

If I open the .sln of the unity project itself, it is no problem. I just can't open the .sln for the windows phone built. How do I solve this?

Thanks