I have 4 USB ports on my PXIe-8105. One port is for an Epiphan frame grabber another port is for keyboard/mouse. The remaining 2 ports are each for a ThinkLogical fiber optic USB extender pair (consists of a transmitter and a receiver). I have 4 Passmark test modules on each receiver. Our test requires us to cycle power to the receiver end of the USB extenders. After several power cycles the PXIe-8105 USB ports for the extenders stop responding. The USB ports for the frame grabber and keyboard still function. The number of power cycles required to repeat the "lockup" varies. I have tried to unplug the extender from the PXIe-8105 USB port and insert a thumb drive. The thumb drive is not found. I have to reset the PXIe-8105 to regain access to the USB ports. How can I determine why the ports lockup?