Norton Ghost 15 "Unable to write to file" (EBAB03F1)

Norton Ghost 15 used to work OK for me (in 64-bit Windows 7). But now, whenever I try to make a back-up, I get the following...

--Unable to write to file.

---Error EBAB03F1: The system cannot find the file specified.

---Unable to write to file.

----Error EBAB03F1: The system cannot find the file specified.

(UMI:V-0-2001-31)

When this happens, the AutoPlay window for the back-up drive appears, suggesting that the connection might have been interrupted.

I've tried the following...

1. clicking for "More Help on the Web" (but that takes me to a page that says I need to upgrade, when I already seem to be using the latest version - 15.0.1.6526)
2. running a disk check on the back-up drive
3. shortening the USB chain
4. deleting my back-up job, and recreating it from scratch
5. reinstalling Norton Ghost
6. checking the status of the relative services

But nothing has made any difference. Can anyone suggest what might?

Thanks.