Yes - I had 'Run as administrator' and the usual UAC box had popped up.
It has obviously messed up permissions somewhere. If I go to C:\Program Files\Affinity and look at the properties of the Publisher folder I get "You must have read permissions to view the properties of this object". Clicking the advanced button then the UAC Continue button gives "You do not have permission to view or edit this object's permission settings".
If I look at my 'Designer' folder, all the permissions, etc look normal.