Nobody can help you with just this explanation. Can you post the demo, so we can try to find the problem!? Did you tried running the game with -diag?

Although you say the client runs games like F.E.A.R. and BioShock. We do not know anything about the computer and OS/hardware/DirectX/drivers of your client. Furthermore, which version of GameStudio are you using? A5,A6,A7? Lite-C beta/final?

Think if you could post more details and maybe a demo (what flits mentioned) perhaps it can be solved