Sorry we fixed the problem on our own
It was Game-ranger, a multiplayer program for MAC similar to Gamespy. There was a new version released, and when the server was started from game ranger or even if it was running in the background, it somehow modified the data in Ghost Recon causing people not joining through Game Ranger to get a wrong software version error. hope this can help a few more troubled people so they dont have to bang their heads against any walls!