WD Backup does not write to disk

I have a 1GB Passport Ultra attached to my PC, which I have used for about 3 years now with no problem. During a recent backup however the PC crashed, since when there has been a problem with the backup routine.

WDBackup will start on schedule, scan my HDD and determine what files need to be written to the Passport as normal. Let’s say there is 15GB to be written… WDBackup then displays a status message saying “Writing 0MB of 15GB…” or words to that effect, but after that nothing happens - the message is never updated and Task Manager shows little or no activity on the Passport. It just sits there for ever…

I ran chkdsk /r on the Passport and this did find and correct some corrupt file indexes etc. Subsequent disk checks reveal no apparent residual disk problem.

How can I determine exactly what the problem is and what to do to correct it ???