suddenly, my books will not transfer to the Nook, would it be a USB cable problem?
If the USB cable is ok the Nook should show up as a drive in Windows Explorer (or Finder on Mac).
That should help decide if it is a cable problem, or another problem.
Did you just downgrade from the reliable ADE1.7.2 to the unreliable AD2.0?
If so, revert to 1.7.2.
Retrieving data ...