Solution : https://service.sap.com/sap/support/notes/371396 (SAP Service marketplace login required)
Key words : 
additional key words bop, t100press 'maintain' buttonmessage class, > > > release 31imessage class cave > > >, release 40abutton 'change'message, prerequisites program error solution, apo backorder processing, 005message short text, requested quantity corresponds, /original requested quantity, sourcing main item
Related Notes : 
       
| 375193 | Backorder processing: Composite SAP note on posting | 
| 372608 | Backorder processing: Temp. quantity assignments not removed | 
| 372123 | Backorder processing: Update is incomplete | 
| 371628 | Manual backorder processing in APO for R/3 orders | 
| 357400 | APO initial provisioning for changed products |