Solution : https://service.sap.com/sap/support/notes/555534 (SAP Service marketplace login required)
Key words :
'change activity element number' context, assign double activity numbers, original activity element number, changethe activity element number, activity number reason, respective main activity, purely numeric numbers, project planning board, termination message co888, form routine check_itab
Related Notes :
| 494969 | CJ2B:activity number change in the table section |