Solution : https://service.sap.com/sap/support/notes/628048 (SAP Service marketplace login required)
Key words : 
terms ps-bapi, source code correction, plugin system 2003, light scheduling, activity data, capacity planning, co_bt_afvg_update reason, program error, related note, solution implement
Related Notes : 
       
| 634869 | SAPKU40001: Support Package 01 for CRM 4.0 | 
| 628033 | RI: Dates for activity element not correctly transferred | 
| 607000 | Required notes for PS-BAPIs |