Copying to external USB drive in Mac OS X 10.8.2 yields "Device not configured" and hard lock
The most common problem with external usb drives are the small power adapter with 2A. I have various WD Drives and all give up after a time with the same error "The disk was not ejected properly...". Without power the hd disconects (for a short time). I bought a bigger power adapter with 3 A and have no problems any more.