SAP Message RP644 - Tab. T521 was changed (please delete payee key)

Diagnosis
The overwrite indicator in table T521 was changed from 'T'
to ' '. This leads to deletion of the stored bank country, bank
number and account number fields when the record is saved
again. To prevent this from happening, you can delete the
payee key or reset it after having undone the change in T521.

System Response