From what I can take from it, you'll require to update the game. If it doesn't update automatically try to verify the game Cache.
Quote:From the Library section, right-click on the game and select Properties from the menu.
Select the Local files tab and click the Verify integrity of game cache... button.
Steam will verify the game's files - this process may take several minutes.
Message back once you have done this to see if it has worked or not.