CnC3 problem

I've been trying to play Tiberium wars on lan with my friends but always when I am in the game everybody gets an Out of synch error and the game ends. When I'm not in game (and 4 of them play), everything is ok. It is certainly me, cause we've tried several combinations and the game freezed only when I was in it. I searched on google for any kind of help, but no success.
We're running the latest update 1.09.
Does anybody have a clue what might be causing this ?