How to get rid of this steam error?: This game is currently unavailable?

I've been getting the same error on Cities XL 2011 for 6 months now. Whenever I try to load it up, I get an error that says the game is currently unavailable. I've tried deleting the .blob file, verifying the game cache, and reinstalling both steam and the game several times, but nothing I do seems to work. Is there any other way to get this game to work?