SAP Message WU220 - Supply sources changes not possible for mat. &. Alloc. table generated

Diagnosis
In an allocation table was generated for a promotion item, the sourcesof supply for the item cannot be changed.
The sources of supply assigned in the promotion are used in theallocation table when data is stored. A subsequent change to thesources of supply would lead to inconsistencies in the promotion. As aresult, the system does not permit you to change this data onceallocation tables have been activated/generated.

System Response
INCLUDE ISR_VERARBEITUNG