SAP Message RE198 - You cannot change the reference to document &1 &2 (see long text)

Diagnosis You want to change the reference to document &V1&, item &V2&. This isnot possible because the document had already been reduced and theindicator Account assignment changeable is not set in eitherthis document or the predecessor document. System Response Procedure If you want to change the reference to the document &V1&, item &V2&,you have to set the indicator Account assignment changeable ineither this document or the predecessor document.