First, let me just say that sometimes it could be the server that is different from the client, but if this keeps happening there are a few things you could try:
- In Steam, select the game, then
Right Click->Properties
, go to the Local Files
tab, and click Verify Integrity of Game Cache
. If steam finds any outdated/missing files, it will inform you and start downloading them.
- Browse to the
steamapps
folder, locate your copy of MW2, and inside /main
, delete (or cut out) all the iw_XX.iwd
files. re-run the verify integrity. It should pick up the missing files and re-download them.
Finally, the most drastic:
Right Click->Properties
, go to Local Files
, and Delete Local Game Content
. Once it is done, go into steamapps
and make sure there are no remaining files. If there are (shouldn't be), delete them. Then re-download the game.
I got stuck with the last option on MW3, it sucked, but luckily I had the game discs (I bought it retail). I just installed off them and then let steam run updates.