Game unavailable

My copy of RtCW will not start. Even though it says 100%-Ready in steam when i click it i get the message "This game is unavailable. Please try again another time". I've tried deleting and re-downloading it but get the same error. However, the first time I tried loading it it crashed on startup saying its stopped responding. That's when i started receiving the unavailable message.

I have Win 7 64-bit and latest nvidia drivers. Does anyone have any idea why this might be happening?

Edit: I can access multiplayer, and when i click on the singleplayer button it spits out a 'could not start process' error, and gives the file path string. No idea why this is happening.

wish someone knew what the problem is. I try to run single player and my user account control tries to confirm the program. I hit accept and it just keeps asking me over and over until I say cancel a few times. Then I just get the Game Unavailable message.

Also, I can access multiplayer but not go to single player from there as well