SAY WUUUT?ava ijji reactor
What the f*** is that? And it sounds pretty scary that it wants to delete steam.exe.
Anyway, I think you may be able to fix your problem by running the ava ijji reactor as adminstartor (Right click -> Run as adminstrator)
If you just wanna play MW2 you should use aIW. Just google it... alterIWnet. A free alternative to IWnet