Solution : https://service.sap.com/sap/support/notes/1056150 (SAP Service marketplace login required)
Key words : 
system issues messages ks 370, fiscal year variant, -calendar fiscal year, master data object, ks 370 reason, controlling area, cost center, cost element, activity type, business process
Related Notes : 
       
| 1178736 | GU 505 unjustified when deleting cost element | 
| 980393 | KS02: Mid-year change to fiscal year-dependent fields | 
| 672255 | Shortened fiscal year/changing fiscal periods |