Solution : https://service.sap.com/sap/support/notes/177520 (SAP Service marketplace login required)
Key words : 
include lcobou43 replace field afvgd, additional key words cn21, activity element, changed data, choose enter, dependent documents, purchase requisitions, program error, solution note 126656, source code
Related Notes : 
       
| 126656 | PReq deletd for external elemt/cap.requments deletd |