[Scorpious2k]

There really aren't enough clues here.

Is the computer you can enter world with the same computer you are running the server on?

Is the exact same client in use on all computers? Same operating system? In other words how are they different?

Are you in a zone with the one that works when the others fail? How many zones (zone.exe) are running?

This is a start. There are a lot of other things that may need to be known, but these will give a chance to find some issues that could be wrong.