I think I may have fixed it or at least discovered what might be the problem.
If I right click on the sonar icon and choose properties I see that there are two accounts marked, "unknown"
I'm not sure whether I should remove them or not, my worry is that as I'm running 3 separate drives with 3 separate windows installations it might be that windows 10 has picked those up and they are marked as unknown?
But how/why could it do that? For the moment I've given those accounts full permissions and will see if that solves the issue but if anyone can suggest whether or not it's safe to remove the two, 'unknown' accounts I would much prefer to do that.
Steve