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
.
Another option, a bit less obvious, is to save the devenv.sln file to the Visual Studio IDE folder for that version of Visual Studio. This was an option described in the link noted above.
Probably not the best option, but it is an option none the less.