Comparing PR quantity with PO quantity

Hi Experts,

I cannot put system message 06 076 as Error because most of the times when purchase order acknowledgment comes quantity will be little more than PR or ordered quantity. If we put 06 076 as error message POA will fail. However we don't want to use one PR more than once.

Can you give me a solution for accommodating above mentioned requirements.

Regards,

John K.