Hmm.. I get this error sometimes on my computer with some of my USB devices. My all-in-one card reader seems to enjoy screwing up the USB drivers, and causing windows to not recognize most of anything I plug into the USB ports. But this is an unrelated issue. But it does prove that its not always a hardware fault. I always got around it by using my USB 2.0 Hub. Since Windows never seems to have trouble recognizing it. Plus I always leave it plugged in.
Its more of an issue with the USB hub your connecting it to. (yes, the ports on the case of the computer has its own "hub" as well, its just integrated into the motherboard) Try a different USB port. Or try a separate hub if you have one. If you computer has rear ports and front ports, try the rear ports. Usually with most motherboards, the rear ports are on a separate hub then the ones on the front.
You can also try disconnecting your other USB devices and restarting and then plugging in the Fire Card first.
A "device not recognized" can sometimes be a problem with Windows, or a hardware issue. Hopefully its not a hardware issue with the Firecard.
Also, did you try a different computer? If you get the same error on a different computer, them more then likely the Fire Card/USB adapter is defective.