Warning al actualizar la base de datos.

El siguiente warning se presenta al actalizar la base de datos:

[2012-01-27 17:32:27,387][produccion] ERROR:db.cursor:bad query: ALTER TABLE "check_note" ADD CONSTRAINT "check_note_check_note_number_uniq" unique(accounting_bank_id,number)
Traceback (most recent call last):
  File "/home/operador/produccion/server/bin/sql_db.py", line 131, in execute
    res = self._obj.execute(query, params)
IntegrityError: could not create unique index "check_note_check_note_number_uniq"
DETAIL: Table contains duplicated values.

[2012-01-27 17:32:27,388][produccion] WARNING:orm.schema:Table 'check_note': unable to add 'unique(accounting_bank_id,number)' constraint !
 If you want to have it, you should update the records and execute manually:
ALTER TABLE "check_note" ADD CONSTRAINT "check_note_check_note_number_uniq" unique(accounting_bank_id,number)