When I first got my VF2 (1 year ago) only 1 usb stick drive worked on the machine. It was the one that the tech owned. I bought 4 or 5 new ones (including the exact same brand and model as the tech`s) to try but they didnt work either, only that one stick worked. The VFO replaced the main board and everything started working fine. Very weird I thought but now its fine. Here is the thread
http://www.cnczone.com/forums/showthread.php?t=51706
Mark