Intercompany Text-Based Standard Purchase Order from Production Order

Question

We have a business scenario where a material is made in a plant and then another plant performs a service on that material.  The customer wants the purchase requisition that is created from the production order from the producing plant to apply a vendor that is an intercompany vendor.
The issue is, these purchase orders are text based purchase orders.  This process works perfectly when there is a material master.
Scenario:
Plant X = Production Order to make Material A
Plant X = Production Order creates a purchase requisition in Plant X; Intercompany Vendor is assigned
Buyer = Creates the purchase order from the purchase requisition
Error Message: SAP issues an error message that this vendor cannot be used.
We are looking for a way to create a text based purchase order (that represents a service) and assign to a intercompany vendor.

Answer 1

The exact error message we receive is:
Diagnosis
You are entering an ordering transaction involving a vendor to whom a plant has been assigned. Normally, materials would be supplied by one plant to another in such a transaction.
This process involves a delivery and billing document in the SD system. The PO for this appears directly in the delivery due list of the issuing plant (vendor) and therefore does not need to be transmitted.
However, items without a material master record cannot appear in the delivery due list.
Procedure
Items without a material master record can only be ordered from vendors without a plant assignment.
The point is if we create a vendor without a plant assignment, how can the inter-company posting be accommodated.