Wow, I'm amazed by the rapid response - and on a weekend, too!!
I ran Defraggler with the /debug3 switch.
I then performed the following operations:
1) Check drive
2) Analyse drive
3) Defrag drive.
Operations 1 and 2 completed successfully.
The resulting log file is currently 946 646kb in size. Not sure if you want me to post it here (not sure if this will even be possible with such a large log file). Please advise.
However - the defrag operation is currently still running, and I see it has progressed to 1% (previously it didn't get this far before failing). I have no idea what might be going on here.
Thanks for your assistance!