Re: Phase2 failure message with there was preexisting session from the same peer

On the SRX, please make sure the 'Untrust' zone interface is permitting inbound ike.

"set security zones security-zone Untrust interfaces fe-0/0/0.0 host-inbound-traffic system-services ike"

 http://forums.juniper.net/t5/SRX-Services-Gateway/Site-to-Site-VPN-SRX100-to-SSG520-stuck-in-Phase-2/m-p/268622

Hope this helps.

Regards,

Sam