CCleaner hangs cleaning external HD

New to this board and distinctly non-technical, so please excuse if a ferdy. The issue is that CC hangs at 36% cleaning my external hard drive (used by backup software) in the recycling bin only.This happens when:

the deletion is set at above "normal",

irrespective of whether or not the backup software is running at the time,

I have not changed any other CC settings.

Many thanks