When I try to get into a certain client within business tax I get the message:

The current list of partners leave the following period(s) of time with no partners or sole trader assigned.

06.04.2021-01.09.21

The business must be a sole trader or partnership at all times.  Until a valid sole trader/partner list is entered this business cannot be processed further.  Please return to Control Centre and modify the partners' joining/leaving dates.

It then boots me out.  The only places I can see in control centre to add dates is 'additional details' began trading/ceased trading.  It worked the other day but now it doesn't and nothing has been changed.  If I change the began date to 06.04.2021 that makes no difference.

At a loss.

Thanks