This message generally means that the pre-shared key values do not match between the two firewalls.
Message: IKE <ip_addr> Phase 1: Rejected an IKE packet on ethernet1/2 from <ip_addr>:<port> to <ip_addr>:<port> with cookies <cookie> and <cookie> because Phase 1 negotiations failed. (The preshared keys might not match.)
Meaning: The Phase 1 preshared keys do not match.
Action: On both the initiator and responder, re-enter the Preshared Key in the IKE gateway configuration.
http://kb.juniper.net/InfoCenter/index?page=content&id=KB9238