The usual course of action is to go onto control panel/hardware and sound/device manager and delete all usb keys then reboot and allow windows to rediscover them.
A less draconian solution that worked for me is to map your USBs using a microsoft utility called usbview downloadable from Future Technology
http://www.ftdichip.com/Support/Utilities.htm
This identifies what each of your USB's is doing and what device is attached. With a bit of detective work to see what other of your devices are adjacent to the "unrecognised" device it is straightforward to identify the specific source of the problem. Disconnect it and reboot your machine to "clear" the error message.
In my case all I then needed to do was remove and replace the driver with the latest compatible from the makers web site, reboot and I was away, but I have read threads where it was badly written drivers causing the problem, in which case your only recourse is Microsoft's own generic drivers which may or may not offer a solution.
martinloat