Instead of writing code in MB_DOCUMENT_BEFORE_UPDATE,write a check in user exit MBCF0002.This exit is having all the required parameters and also it will trigger while checking document and also posting document. We can use '' sy-cprog'' to judge whether to use Validation Logic...
Solved: Hi, I implemented the BADI MB_DOCUMENT_BADI - Method MB_DOCUMENT_BEFORE_UPDATE. Inside the method I called a custom Function Module which calls a BAPI