Arma 2 won't open

[FirePanda 1]

I just finished installing Arma 2 combined OPs off of steam, and now I can't open it. When I try to open it the loading bar stops at the last check mark and an error message pops up, something about the wrong addon for DirectX I think. I don't know how to fix it, has anyone else had this problem?

---------- Post added at 13:21 ---------- Previous post was at 13:20 ----------

Here's the error message

[Placebo 31]

That sounds like a corrupt download. Exit steam, reboot, disable any antivirus, launch steam as admin http://img717.imageshack.us/img717/5892/steamadmin2.jpg then right click operation arrowhead in the library and go to properties/verify cache integrity.

[FirePanda 1]

Thank you Placebo, that was the problem

[Placebo 31]

Yay :)