Seen this pop up a few times now, if Verify Integrity of Game Cache doesnt fix it try this.
http://steamcommunity.com/app/10/discussio...76145695500523/QUOTE
Exit Steam entirely.
Browse to your Steam installation (Usually C:\Program Files(x86)\Steam\)
Rename the "steamapps" folder to "old_steamapps"
Re-launch Steam and re-install the game.
Once the installation is complete, test the issue.
If this resolves the issue, you may copy the new files into the "old_steamapps" folder and rename it to "steamapps" to restore your other games without re-downloading.
If the issue is not resolved, you can rename the folder back to avoid having to re-install other games.
--------------------------------------------------------------------------------------------------------------------------------------
If renaming the "steamapps" folder and reinstalling the game resolves the issue, you may do the following to restore other games without re-downloading them:
Exit Steam entirely again.
Open the "steamapps" folder, press CTRL+A (select all), then CTRL+X (cut).
Open the "old_steamapps" folder, and press CTRL+V (paste). This will move all of the new files into the old folder.
When Windows asks, allow files to be overwritten with the new ones - this will replace corrupted files in the "old_steamapps" folder.
Delete "steamapps" and rename "old_steamapps" to "steamapps"
Re-open Steam and your games should be restored in working condition.
If you have any further questions, please let us know - we will be happy to assist you.