Problem with Delivery Type Determination in Purchase Order

Dear All,

We are working on a IS-Retail Scenario where we are dealing with generic articles. While creating a PO, we have encountered an error which says:"Also specify a delivery type in case of shipping data relevance". The error message number is MEPO 099. We have checked that Delivery type NL is attached to the document type under the supplying site customizing, and supplying site is attached to the receiving site with the correct document type. Can anybody throw some light on what we might be missing out in this scenario?

Thanks and Sincere Regards,

Amitabha