I am trying to import the updating data for the contact list using my old import file. Just for updating the language of the contacts.
But it's failed. I got the error of  'Error at row 7: "duplicate key value violates unique constraint "res_partner_bank_unique_number" DETAIL: Key (sanitized_acc_number, partner_id)=(4831509690833, 24221) already exists. '  for many rows. 
What exactly does this error refer to?