I just encountered a strange behaviour in my Visual Studio 2010 installation. Out of the blue I was no longer able to open more than one file in one tab at the same time. This is obviously very annoying if you work on a project wich includes several source-files (which is the general case I guess). After some googling I found a solution that helped me without reinstalling everything:
just type at a VS 2010 command prompt (open it from the start menu)
devenv /ResetSettings
This will open the VS 2010 IDE and resets all settings that you may have made. After that everything worked like a charm again.
cheers
