Solution : https://service.sap.com/sap/support/notes/503040 (SAP Service marketplace login required)
Key words : 
system generates message mn227, settlement document 'subsequent settlement', 'error determining data, business volume subject, volume-based rebate, euro-change occur, company code currency, rebate arrangement currency, attached program corrections, vendor billing document
Related Notes : 
       
| 502747 | Settlement via credit memo: Message MN178 | 
| 183379 | Composite SAP note subsequent settlement (Purchasing) 4.6 | 
| 152725 | Collective note: Subsequent settlement (Purch.) Release 4.5 | 
| 104668 | Collective note: Subsequent settlement (Purch.) Release 4.0 | 
| 40147 | Collective note: Subsequent settlement (Purch.) Release 3.0 |