On Windows 7 Pro x64, the customer has a USB3 external Hard Drive that is 2TB, and two internal SATA drives that are 750GB each. They also have a USB controller, which the hard drive is plugged into. It fails at around 30% with "Error 80070037". No real details given, other than it can't find the device. I disabled power save mode on the device, and in the BIOS, but same error occurs. I formatted the drive and tried again, but no dice. I went through the backup settings, and told it to back up the entire system, and it starts, just to end again around 30% with the same error.
Currently, I am CHKDSKing the computer, and using the Western Digital DataLifeguard on the external drive. Will post back with results
UPDATE Chkdsk came back clean. Hard drive is fine. Waiting for WDDLG to finish on external, then I will try the USB port mentioned by @Moab
UPDATE 2: External hard drive checked out fine. Trying on USB 2 port now...