Что происходит с IPSec???
По логам она рвется постоянно. Параметр keep alive - enabled (auto)

2012-05-24
04:59:53 Info IPSEC
1802708


ike_sa_destroyed
ike_sa_killed
ike_sa=" Initiator SPI ESP=0xfcf65faf, AH=0x11559c28, IPComp=0xd3f9dbf"
2012-05-24
04:59:53 Warning IPSEC
1802022


ike_sa_failed
no_ike_sa
statusmsg="No proposal chosen" local_peer="127.0.0.1 ID No Id" remote_peer="46.38.53.51 ID No Id" initiator_spi="ESP=0xfcf65faf, AH=0x11559c28, IPComp=0xd3f9dbf0"
2012-05-24
04:59:53 Warning IPSEC
1802715


event_on_ike_sa
side=Initiator msg="failed" int_severity=6
2012-05-24
04:59:52 Info IPSEC
1800317


peer_is_dead
IPsec_tunnel_disabled
peer=46.38.57.251
2012-05-24
04:59:52 Info IPSEC
1802708


ike_sa_destroyed
ike_sa_killed
ike_sa=" Initiator SPI ESP=0xc6652651, AH=0x9fe4dae9, IPComp=0x2af434a"
2012-05-24
04:59:52 Warning IPSEC
1802022


ike_sa_failed
no_ike_sa
statusmsg="No proposal chosen" local_peer="127.0.0.1 ID No Id" remote_peer="46.38.53.51 ID No Id" initiator_spi="ESP=0xc6652651, AH=0x9fe4dae9, IPComp=0x2af434a7"
2012-05-24
04:59:52 Warning IPSEC
1802715


event_on_ike_sa
side=Initiator msg="failed" int_severity=6
2012-05-24
04:59:50 Warning ARP
300009


arp_resolution_failed
remove_entry
ipaddr=192.168.11.163 iface=lan
2012-05-24
04:59:43 Info IPSEC
1802708


ike_sa_destroyed
ike_sa_killed
ike_sa=" Initiator SPI ESP=0x897a52ae, AH=0xa391107f, IPComp=0x8e3e71e"
2012-05-24
04:59:43 Warning IPSEC
1802022


ike_sa_failed
no_ike_sa
statusmsg="No proposal chosen" local_peer="127.0.0.1 ID No Id" remote_peer="46.38.53.51 ID No Id" initiator_spi="ESP=0x897a52ae, AH=0xa391107f, IPComp=0x8e3e71e3"
2012-05-24
04:59:43 Warning IPSEC
1802715


event_on_ike_sa
side=Initiator msg="failed" int_severity=6
2012-05-24
04:59:42 Info IPSEC
1802708


ike_sa_destroyed
ike_sa_killed
ike_sa=" Initiator SPI ESP=0x13acf95b, AH=0xf8b9874f, IPComp=0xf9ddeb8"
2012-05-24
04:59:42 Warning IPSEC
1802022


ike_sa_failed
no_ike_sa
statusmsg="No proposal chosen" local_peer="127.0.0.1 ID No Id" remote_peer="46.38.53.51 ID No Id" initiator_spi="ESP=0x13acf95b, AH=0xf8b9874f, IPComp=0xf9ddeb83"

Нет идей?

Из-за чего такое может быть?

попробуйте снять галочку Dead Peer Detection с обоих сторон (закладка IKE settings , внутри IPSEC тунеля).