Suddenly unable to open MPQ (PC/Steam)

Unknown

So it was working fine this morning. No updates went through or anything, but when I got home this evening and click to play it brings up the "Marvel Puzzle Quest has stopped working" dialogue and then closes out. Can't even get to a loading screen. Did the whole rebooting thing, of course, and verifying the files through steam and everything looks good. Just won't load anymore.
Anyone else with this issue at the moment?


Edit: Nevermind. Just did some checking, it seems that Valve have screwed something up and a lot of Vista users cannot load many/any games currently. Might be fixed tonight, might not. YAY! At least it's not a D3 issue.

Edit 2: It's a Steam Beta update that caused the issue. I knew I shouldn't have opted in. Sigh.