Remembering that it did start working after a 'clean sweep', so this is 'history' now and I obviously had done something wrong (some sort of clue from the OS would have been nice).
Mr O - tried both
Milo - I did get a log-in prompt at one point, no network drive involved, just a 'straightforward' (if only!) attempt to view the host from the client, and it saw the request as 'Guest' and entering that p/w worked.. BB in post#5 seems to agree.
Avast and ZA, both disabled/fiddled with etc but not uninstalled, but I repeat, with the same settings on both NOW it works.