10/10 - Bacon saved!!! Many thanks.
You were absolutly right, although these "phantom" duplicates were not showing in the Pastoral Structure it was indeed the problem. All now fixed, the office staff just need to fill in Registration \ Lessons from the paper copies for yesterday & this morning.
We just went through the motions of "Reuse old registration groups" this produces a new one of same name, remove the origional (moving any "members" to new one) adjust any incorrect Registration Tutors names, save and all was fine again.
Cheers,
Peter