Diagnosis
You have tried to copy an order item to the delivery, when the item inthe order was created as a result of product selection. The reason forsubstitution, however, requires that this item is not to be copied, butis to be created in the delivery nby means of a new product selection.This is a contradiction.
A possible reason for an unwanted transfer of the sub-item is that theschedule line category of the respecive schedule lien is relelvant fordelivery.
If you do, however, want to transfer the sub-item from the order, youneed to set the event to 'B' in the reason for substitution.

System Response
The system gives the reason for substitution a higher value. It doesnot copy the sub-item from the order, but carries out a new productselection in the delivery.

Procedure
Check in the order or in the condition record for product selection (inthe master data for Sales) to see which reason for substitution hasbeen used.
In Customizing for product selection, check to see which event is usedfor the reason for substitution that was enployed.
Sales and Distribution -> Basic Functions -> Material determination ->Define substitution reasons
Check in the order to see which schedule line catogory the schedulelines of the found order items have and check in Customizing that theschedule line category used is not relevant for delivery.
Sales and Distribution -> Sales -> Sales documents -> Schedule lines ->Define schedule line categories
Make sure that the schedule line category is not relevant for deliveryand the event of the substitution is not 'A' at the same time.