Defraggler DF.EXE runs forever

I created a batch file so I can defrag several drives overnight.

It displays the output in a DOS window.

The first few drives finished fine but when it got to drive F: it looks like it is processing properly.

It said:

Degragmenting drive F:

Building File List Started

Building File List (0%)

...

Building File List (100%)

Building File List Complete

Defrag Started

Defragmenting (1%)

...

Defragmenting (100%)

and it stays there without updating the screen. There is no "Defrag Complete" or "Finish" messages.

Drive F: is a backup drive for Acronis backup files and Acronis was NOT doing a backup at the time so nothing was writing to that volume.

The next morning the hard drive light is still on continuously and I let it run for another 8 hours. So something is evidently wrong. I had to Ctrl-C the program. The pagefile is on drive G:, the next drive in the list. So what happened? :o

TIA