I can't start the game through the Steam client. It gives me a "Failed to start game (unknown error)." message. Had it under the previous version as well. However, I can start the game from the game directory directly just fine. Steam overlay works, game performs fine.

The SupportTool.exe file is likely the culprit since it does not start at all but gives the following error: http://i.imgur.com/uJusCGP.png?1

I have no idea how to fix it since verifying the game files through steam doesn't download any new files and the error happily occurs again.