Hey, My friend has a problem that every round when RED win the boss he gets some kind of picture with flickering color that blocks his screen, and only when he Re-Joins the server he can play, but then again when RED win this picture shows.
Any one knows how to fix it or what might cause the problem?
By the way its only on that server.

This is the first report of anything like this, which suggests it's client related. I suggest that your friend tries updating graphic drivers, removing any interface customisation and scripts. There is nothing within FF2 that displays an image at the end of each round.