How can I 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 several times, but nothing I do seems to work. Is there any other way to get this game to work?