Solution : https://service.sap.com/sap/support/notes/66925 (SAP Service marketplace login required)
Key words : 
additional key words ko88, unjustified error messageaw639, order/wbs element, controlling area currency, wbs element, internal order, transaction currency, controlling area, periodic settlement, investment measure
Related Notes : 
       
| 77032 | AW639, if several depreciation areas for revaluation | 
| 75405 | Inv meas sttlmt -> AW639 or AuC deprec areas wrong | 
| 71699 | AW639: Additional security check | 
| 68839 | Settlement to fixed asset with group assets->RW022 | 
| 60619 | AW639 when settling investment measures | 
| 40041 | Settlmt of cap.inv.meas. -> message AA641/AW639 |