SAP Message AJ526 - Cannot reset document number &1 due to re-billing &2

Diagnosis
Billing document &v1& cannot be removed from the corresponding billingcontract, since it no long exists due to new billing &v2&.

Procedure
Read the report documentation for report REASCBEL for information onthe conditions for undoing the billing reversal.
You might have to reverse other actions that occurred after the billingreversal, such as the new billing.