I find that USB sometimes stops recognizing new devices after my machine has been running for a while. I don't think that it has ever been a problem after a fresh reboot. This isn't normal behaviour but it hasn't bothered me enough yet to try to resolve it. In your case, I suggest that you try it after a reboot and see what happens. If that consistently works then it provides more info and a way to get around it until you get a better resolution.
[I am using Win 7 on a 64 bit machine.]
chrishea
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