PDAMan:Thanks folks, I'm going to have to come back to this in a couple of days.
Mauricio, I already had that selected but most of my files on Onedrive are data on my D Drive, particularly photos and videos, so I assume they don't have a footprint on C:
As to the suggestion of moving Band in a Box to D, or another partition, I thought programs had to run off C Drive. Has this changed?
Programs can be installed and run from wherever you want, granted that they aren’t hardcoded by an amateur developer.
Was going to ask if you were a linux user since what you’re attempting (adding space from another physical disk to a different partition) can be done with lvm, though it’s not always recommended to span logical volumes across physical media.
I would run though some of the advice in this thread to see what is taking space in your system drive, possibly move it around to your other drives to free it up.