SAP Message TU521 - Portion &3 of contract &1 does not correspond with portion &4 of contr &2

Diagnosis
You have tried to execute a function (such as copy payment plan forsupplier change) for which it is necessary that the portion (&V3&)allocated to contract &V1& is identical to portion &V4&, which isallocated to contract &V2&.
In this case, this condition has not been fulfilled.

System Response
INCLUDE ISU_VERARB OBJECT DOKU ID TX