Hi Remy
When you say calculate forecast in SDP94 you mean there is a macro which is doing this, right? If yes is this a start, default macro etc.? Are you not executing this macro in background in process chain itself? If not then create an activity with this macro, create a job for this activity and schedule the same in process chain before transferring data to ECC. Make sure planning book is separate for this job and for transfer of forecast.
regards
Rahul