A.R.S.E.

Haven't come across the black screen one specific to AMS2. Sounds like a video card driver crash. If he hasn't already, he might need to do the usual update gfx drivers with the clean install option.

When hosting multiplayer make sure the ratings system is turned off. It's the cause of the really bad stutters/freezes. Seems to get worse the more players are on the server.

Do you have safety rating turn on Durbs? That's a bad one for stutters.