I couldn't back up my computer using my BUFFALO HD-PNFU3 1 TB MiniStation. It had worked fine for years, but recently when I plugged it into my USB port and moused over the Backup Utility icon, I saw the message "Backup Destination F:Not Connected".
Trying different USB ports or restarting my computer didn't help. I finally found a solution: uninstalling and reinstalling the Backup Utility software.