Solution : https://service.sap.com/sap/support/notes/677756 (SAP Service marketplace login required)
Key words : 
support package level, execute function 'schedule', img transaction opuc, 'illogical' required entries, project planning board, set indicator 'field, attached program corrections, required entry', project builder, opuc reason
Related Notes : 
       
| 679226 | CJ2B: Termination with message CO888 during saving | 
| 609427 | CJ2B: 'Illogical' required entry field check on saving |