You might want to contact the vendor from whom you purchased it for a replacement. In our testing, we have run across a couple with this problem, so we always give them a quick test before they get shipped. They are a low-cost unit and don't see much in the way of QC from the manufacturer.
These should work fine on Win7, 32 or 64 bit versions. Usually an "Unknown Device" error on an HID device indicates that the system has detected that something has been plugged into the USB port, but the device is not actually communicating it's information to the PC. IOW, improperly functioning device. Having repaired a couple, I can say that the cause is likely a poor soldering job on one or more of the components. You also want to try the unit with a different cable, just to make sure it's not the culprit. The cables are prepackaged, and a bad one could also be responsible for this kind of problem.
RandyT