Diagnosis
You wish to assign a vendor to additional &V2&using workflow in additionals document &V1&. The purchase order hasalready been generated, however.
If an additional can be ordered from a number of vendors, the systemcan generate a workflow entry for selecting a vendor interactively (aslong as the relevant setting has been made in Customizing). This iswhat has happened here.
When generating the additionals document, the system assigns the firstvendor in the list to the document. In the case of document &V1& thisis vendor &V3&, from whom additional &V2& has been ordered.

System Response
The system informs you that a purchase order has already beengenerated.

Procedure
Once a vendor has been selected, the selection cannot be changed. Flagthe workflow as "completed".