Solution : https://service.sap.com/sap/support/notes/39557 (SAP Service marketplace login required)
Key words : 
additional key words subsequent settlement, credit-side settlement type, symptom error message m8050, error message results, volume-based rebate, input tax allowed, subsequent settlement, credit memo, program error, tax category
Related Notes : 
       
| 40147 | Collective note: Subsequent settlement (Purch.) Release 3.0 |