How can you update a System to generate an error message when a user tries to enter two Sales orders with the same reference to the customer's purchase order? | SAP-SD

 You can update a System to generate an error message when two Sales orders are entered with the same reference to the customer's purchase order by doing the following:
?    Enter "A" in the check PO number field under general control in the VOV8 transaction
?    Modify the message category of V4-115 to "E" from "W" in the OVAH transaction