What about ping? The next time you're on, (maybe you've already done this) check the pings of the people that join. If they're above 300 than it's likely that THEY just can't handle Multiplayer. If it they all have low pings though, I don't know what to tell you... I guess just don't host any servers. It's easier to just join a fast one anyway.
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=[SE]= MSgt. Parchy
Screamin' Eagles
Company First Sgt.
http://mohaaplatoon.tripod.com