I have always had intermittent problems with my USB expansion card sometimes failing to initialise or locking up. This would usually happen when starting up the PC and the card would lock up with the LED indicator permanently on - the only solution would be to disconnect and re-connect the USB cable.

As per the Opencockpits documentation The card was connected without an external 5v supply, only the master cards had power supplies connected to them. Out of curiosity I tried connecting a 5v supply direct to the expansion card to see if it made any difference and lo and behold no more lockups! I seem to recall reading posts from others having similar problems with Opencockpits cards so this may be worth a try if you have similar problems.