I have had the same thing happen to me. Right click on the name of the game in Steam and click properties. Then click the "local files" tab and verify integrity of game cache. It takes a few minutes but works after that. Hope this helps

Doesn't work, sadly. Whenever I verify, Steam reports 1 file as damaged and re-downloads it, but the game still won't start. When I re-run the verification, I get exactly the same. It's like Groundhog Day.