False alarm.
I fixed the missinggrid.nl issue and the task behaviour is now correct, but the permission error remains.
Investigations are ongoing.
UPDATE : The error was traced to a bad edit of the app/ancil_lct/rose-app.conf file.
I had inadvertently replaced
default=ants-launch ${CONTRIB_APPS}/LCT/ancil_lct.py ${source} \
with
default=ants-launch ${source} \
because I had earlier replaced the default ancil_lct.py with my own version. Evidently, my edit to revert back to the default version was incomplete.
Stupidity has consequences ![]()