Hi Yoon,
Can you check the selected Planning profile group in Trade promotion and its planning profiles are maintained correctly in CRM and BI/SEM (Transactions BPSO and UPX_MNTN).
Its part of TPM Key figure planning details maintenance in both the systems.
You can save Promotion without selecting PPG in CRM Web UI but it wont have planning details, its part of BI/SEM integration set-up.
Regards
Naren..