Copying to external USB drive in Mac OS X 10.8.2 yields "Device not configured" and hard lock I am copying using cp or mv on the command line a large amount (>500gb) of files each sized between 600MB and 2.6GB to an external drive (a Thermaltake BlacX Duet), but after a significant but inconsistent amount of transfer (e.g. 121gb) the following happens:


A message pops up in a dialog box that says "The disk was not ejected properly. If possible, always eject a disk before unplugging it or turning it off." (There were no physical events that took place that would have resulted in a disconnection) 
The copy fails for an item and all subsequent items, complaining with various errors including:

"device not configured"
"Invalid argument" (because the destination no longer exists)
"No such file or directory" (ibid)

The Terminal locks up
Executing 'Force Quit' on Terminal quits the Terminal, but it cannot be reopened
Finder locks up
No applications will start
Relaunching Finder causes the menu bar at the top and the dock to disappear
Rebooting does not succeed (i.e. one must hard-restart by holding the power button); variations on ejecting (before Finder locks) and unplugging the USB cable appear to have no effect on the inevitability of this result.


Note that roughly the same result occurs when attempting the same copy in Finder. In particular the dialog entitled "Copy" remains open, clicking the "Stop copy" "X" button causes an indefinite pause with "Stopping ..." showing. One can still access the Finder, and even read from the drive, but relaunching Finder causes it to display seemingly indefinitely "Application not responding" and in any case one cannot start new applications.

After rebooting, the destination has received most of the data. Disk utility reveals no issues with the destination drive.

I have Spotlight disabled for the external drive, if that makes any difference.

Obviously the expected behaviour from copying is not to have the computer hard-lock requiring a forced reboot.

For obvious reasons (Terminal being locked, applications won't start) it is hard to diagnose the problem.

Any insight would be greatly appreciated.

EDIT

I have had some success by repartitioning the drive into two main partitions of about equal size (460GB) on the drive at the beginning and end with a medium sized partition in the middle (as it seems that this error is occurring at around the "middle" of the drive size). However, I am uneasy about this very speculative solution. But if it works, I can get on with life. :) In any case, insight into the nature of the underlying issue is most welcome.
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.