Solution : https://service.sap.com/sap/support/notes/1053113 (SAP Service marketplace login required)
Key words : 
system isues error message  /scwm/serial 012 'number, terms serial numbers reason, transaction /scwm/to_conf, confirm serial numbers, attached correction instructions, serial numbers, program error, quantity surplus, solution implement, correspond
Related Notes : 
       
| 1024365 | Missing HU - Serial numbers are not deleted |