IPSec-VPN Site2Site mit Firebox X750e, Encryption bit not set

Hallo zusammen,

suche Ideen zu einem Router-zu-Router VPN-Problem.
Bei der Verhandlung der IPSec-Phase1 (mit AES128, SHA1, Diffie-Hellman Gruppe2, PSK, PFS) kommt Meldung:
...
Sending fifth message with policy [NSN Herentals] to Other-side-IP:500 main mode
Process INFO_EXCHANGE : EncryptBit set before SA created
Cannot process the inform message from Other-side-IP:500 to My-IP cookies i=47d53c1b 9c7706ea r=cfb814d5 6aa4aad8
Received sixth message with policy [NSN Herentals] from Other-side-IP:500 main mode
Process 5/6 Msg : Encryption bit not set
Cannot process MM ID payload from Other-side-IP:500 to My-IP cookies i=47d53c1b 9c7706ea r=cfb814d5 6aa4aad8
...

Jemand ein Hinweis?
Danke für jede Hilfe.