Solution : https://service.sap.com/sap/support/notes/308215 (SAP Service marketplace login required)
Key words : 
additional key words me22n, newly determined partners, transaction me22n, partner determination, purchase order, vendor master, change mode, contract number, update termination, partner roles
Related Notes : 
       
| 431351 | ME22N Change purchase order, no new partner determination | 
| 209767 | ME22N: Partner not determined |