Solution : https://service.sap.com/sap/support/notes/397814 (SAP Service marketplace login required)
Key words : 
attached source code corrections, ' additional key words transaction, transaction /sapapo/c4, error message sr053, 'parameter process' tab, update entries hang, /sapapo/bop_updatebackorder processing, connected oltp system, /sapapo/bop_result, oltp system
Related Notes : 
       
| 419491 | Backorder processing: Method N is not allowed | 
| 397016 | Transfer of logical system in the CIF lookup table | 
| 375193 | Backorder processing: Composite SAP note on posting |