Solution : https://service.sap.com/sap/support/notes/507888 (SAP Service marketplace login required)
Key words : 
negative accumulated atp quantity, negative atp reason, 'parameters process' tab, high correction quantities, prerequisites correction quantities, 'parameters check' tab, /sapapo/rrp 3 tab, perform backorder processing, run backorder processing, backorder processing
Related Notes : 
       
| 375193 | Backorder processing: Composite SAP note on posting |