There may be a stuck wrkrelease record that needs to be reviewed in the SQL Server Management Studio.
Note: As a precaution please confirm recent backups of the SL databases exist before proceeding.
Run the query select * from wrkrelease against the SL application database in SQL Server Management Studio. If you find a record in this table for this batch number delete the record in the table, and go back and try releasing the AP batch in Accounts Payable.