after searching for ages i found this solution
so can someone help with this? :(
If it queues on forever and it says that your playlist is older than the Host (when trying to join a friend's game, do the following:

1-Contact a friend with a version of the game that is working fine

2-Tell him to go to this folder

\Steam\steamapps\common\call of duty modern warfare 2\zone\english

3-Let him copy a file called mp_playlists and send it to you

4-Go to YOUR \Steam\steamapps\common\call of duty modern warfare 2\zone\english

5-Paste and replace