Message SAP BORGR604 - Purchasing document &1 is not valid for an inbound delivery item

Diagnosis
You have entered a purchasing document as predecessor to the inbounddelivery item. This purchasing document cannot be delivered.
Purchasing documents that are valid as predecessor documents forinbound deliveries are purchase orders and scheduling agreements.Inquiries and contracts cannot be entered as predecessors for aninbound delivery.

System Response
The inbound delivery cannot be posted.

Procedure
Enter a valid purchasing document.