Flash Drives Do Not Power On

I have a problem that I would like to solve without an OS reinstall. After a reboot, flash drives work perfectly. Eventually, they turn on for a brief second and then turn back off. This seems to be happening after about the 20th insertion of a drive. They won't work again until a reboot.

Here is the setup:
School Computer Lab
One PC
One 2 port USB Card
One NComputing X550 card http://www.ncomputing.com/product-xseries
Win XP SP3
Microsoft Steady State
6 Stations running off the same PC
6 Monitors with built-in USB Hubs plugged into the on-board USB and the add-in card

This was not an issue when the setup was new but is now happening on 4 systems.

I have reinstalled the NComputing software(4.04.010.4). I have updated BIOS. I have updated the chipset drivers. I have uninstalled all USB components and allowed them to be reinstalled. I have used USBDeview to remove all the references to past flash drives.

The problem happens after many insertions of flash drives. I have counted 22after a reboot before the problem started. It happens on drives plugged into the monitor hubs. These hubs can be plugged into either the on-board USB or the add-in card. If I unplug the hub and plug it back in, there is no change. If I unplug a hub and plug the drive directly in, it stays powered on but is never initialized. Once the problem starts, it is a problem for all drives on all ports except the rarely used front panel ports. If I plug the drive into one of the front panel ports that hasn't had a hub plugged into it, the drive works fine.