Diagnosis
You have tried to create a schedule line for an item which already hasother schedule lines. These exisiting schedule lines refer to ordertype '&V3&'.
The schedule line you just entered has schedule line category '&V1&'.Order type '&V2&' belongs to this category.
The error message occurred because either order type '&V2&' or '&V3&'is empty.

Procedure
Change the schedule line categories so that either all or none of theschedule lines for the item have an order type.