Hi Marian - And thank you
But I've already seen both those "articles" and already done the actions described in them - and unfortunately they don't help with my particular problem.
To complete the quest the "confused ghost" has to be on the Isle of the Dead and in my game he isn't, even though the map marker tells me he is
And I've re-loaded from different previous saves a couple of times and taken different paths back to get back to the Isle of the Dead but the ghost is NEVER there
I think I'll just have to concede that the quest can't be finished