I'm trying to help a coworker and don't know citrix that well, so please be gentle...
We're using v4.5 on 2003 and it appears that they've been rebooting the servers every week to help clear out hung/invalid sessions.
Right now we're seeing an issue on 2 of the servers where users are complaining that they can't get into their sessions or the performance is bad. When we try to list out the sessions with qwinsta or even the Shadow applet, it hangs the utility right after listing the system sessions. If we try to bring up task manager, we see the icon on the taskbar but it never comes up. We can see some users on the server using Power Fuze, but when we do an nbtstat; we see alot more users are connected to the system.
At this point, we're stuck waiting for the weekend so we can reboot the server but it seems like there should be an alternative course of action to recover from this and prevent it from happening in the future.