“iSerialNumber” is the serial number of the drive inside the enclosure, so ISTM that the hard drive is being detected by the USB-SATA bridge IC.
Are you able to detect the drive with a disc diagnostic such as HD Sentinel or HDDScan?
HD Sentinel (DOS / Windows / Linux):
http://www.hdsentinel.com/
HDDScan for Windows:
http://hddscan.com/
Does the drive report its correct model number (WD50xxx) and correct capacity?
