having an issue with a VPN tunnel between a Nokia IP120 running NG FP3.  There are three tunnels to three different sites.  Two tunnels stay up without any issues, one does not.  It keeps giving me the error "Encryption fail reason: Packet is dropped because there is no valid SA"  This troubled tunnel will come up after awhile, sometimes down for 3 hours,  but it goes down about twice a day.