I've often had problems starting IPSEC tunnels (m0n0wall to m0n0wall).
However, clicking "Save" on the "VPN: IPsec" page usually took care of the
problem. After upgrading to 1.2, I now have to uncheck "Enable IPsec" wait a
few seconds and then re-check "Enable IPsec" to get a single tunnel to come
up. They work great once you get the tunnel up but I don't understand why it
is necessary to do anything more than just enable the tunnel, wait a 20
seconds or so, then send a few ping packets. Anyone else fighting
m0n0-to-m0n0 IPSEC Tunnels?