Try all of this:
- Right click on MW2 (in steam libary) select properties, go to "LOCAL FILES", and click on "VERIFY INTEGRITY OF GAME CACHE.."
- Right click on MW2 (in steam libary) select properties, go to "LOCAL FILES", click on "DEFRAGMENT CACHE FILES"
- Run Vac chaos AND steam in admin mode.
- Download 2.10 version of vac chaos. It's at their site (not gonna advertise, use google)
- Delete all files (NOT MAPS!) in "X:\Program Files\Steam\steamapps\common\mw2" (once again, DO NOT DELETE THE MAPS LIKE MAIN AND ZONE IF YOU DON'T WANT TO DOWNLOAD 11 GIGABYTES!)
- Redownload vac chaos.