When you open your solution or project on another PC, you might get the following error:
".csproj cannot be opened because its project type (.csproj) is not supported by this version of Visual Studio."
To avoid the loading problem, you can run devenv.exe /resetskippkgs to clear all options including SkipLoading tag which disables the loading of the VSPackage. Then start Visual Studio. Clearing the tag re-enables the loading of the VSPackage.

Source: http://msdn.microsoft.com/en-us/library/ms241276%28VS.90%29.aspx