SAP Message WS531 - Reversal of document &1 not possible, active follow-on document items

Diagnosis
You want to cancel a document or a document item. At least one item fromthis document has already been set in a follow-on document and is stillactive.

System Response
The system cannot cancel the document or item.

Procedure
First ensure that the document either contains only active items (itemsare not set in a follow-on document) or inactive items (items are set ina follow-on document.)