When I open my solution by double click on solution file in a file manager, Visual Studio 2012 asks me whether I want to save devenv.sln:
As indicated here, you have to configure "C:\Program Files (x86)\Common Files\microsoft shared\MSEnv\vslauncher.exe"
to run as Administrator.
C:\Program Files (x86)\Common Files\microsoft shared\MSEnv\VSLauncher.exe
I also did the same for C:\Program Files (x86)\Microsoft Visual Studio 11.0\Common7\IDE\devenv.exe
.