OK. Guess nobody has info... ?
The problem disappeared on deleting hts-nohup.out.

I've not a clue what this file does and found only one ref in this forum about
stopping its creation by making a similarly named directory instead. Haven't
found any docs or other info on this file. Don't know why this file would
cause the pgm to quit and complain about "can't somepath/hts-log.txt..."

Life is full of mystery.

Cheers, Rufus