Solution : https://service.sap.com/sap/support/notes/556036 (SAP Service marketplace login required)
Key words : 
implies incorrect cost distribution implies alack, handle retro active calculations correctly, employees earliest retro date, terms xdec costs reason, selected public sector clients, budgets/pay scales, respective government bodies, gb payroll cluster, historical pay periods, retroactive payroll runs
Related Notes : 
       
| 642937 | Syntax error in RPCALCG0 after upgrade to R/3 Enterprise |