Thanks @Grayden_Shand
The error has gone.
If I may pick your brains a little more, do the tallies generated by this query include posts by email, and replies by email for users on email list mode? If not, how can I include them?
Also how can I include the value of a custom user profile field beside the user’s name?
Are there any tips you can offer as to how to identify the field name involved, and implement this?