Social workers had to stop practicing after forgetting to register with their national body.
Staff employed by Norfolk County Council's children's services department were sent an email last year telling them to remember to register with professional bodies after several had forgotten.
It is illegal to practice as a social worker without being registered with the Health and Care Professions Council (HCPC).
The email from May read: 'There have been a few instances where those who require registration with a professional body in order to carry out their duties on behalf of the County Council have allowed their registration to lapse.
'You will not be able to continue you work for Norfolk County Council during any period that you do not have the registration.'
A council spokesman said: 'None of our social workers will be practicing without registration being in place.'
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