Hi Neil,
This is on Windows 7. I am not sure if it is Fences, that could be. I *think* I disabled Fences while I was trying to fix this, but I can't remember now. I do know uninstalling Deskscapes does fix it. Reinstalling then has everything working again.
This is not the first time I have uninstalled Deskscapes due to this problem. Works for a while then kaboom the problem comes up again. It is a strange bug somewhere for sure one way or another!
Thanks for your help.