Purchase Order Created even validity date of Contract is already expired

Issue :
purchase order is created for non valid contract ( validity date of contract is already expired) but still it is creating Purchase Order in reference to contact.

I also checked the source list if its validity date is more than the contract. But the source list is not maintained for this material.

Solution:

Go to T code OLME ->Environment Data ->Define Attributes of System Messages->System messages

Here make sure System message no 06 040 and 06 041 is set as error (E).

so that user cannot create PO outside contracts validity period.