Solution : https://service.sap.com/sap/support/notes/371628 (SAP Service marketplace login required)
Key words : 
rules-based check occurs, attached source code corrections, additional key words, requirement errors occur, subitems occur, apo system, backorder processing, sales orders, generate subitems, prerequisites note 367039
Related Notes : 
       
| 375193 | Backorder processing: Composite SAP note on posting | 
| 371396 | Update of BOP results | 
| 367039 | Sales order entry, sourcing, third party processing |