I'm still trying to figure out why my Cisco certificate-based VPN won't work with the built-in OS X VPN client. It works great on my iPhone, but not on my mac.

same. i get the generic error:

VPN Connection
Could not validate the server certificate. Verify your settings and try reconnecting.


In my console log:

10/28/09 1:23:06 PM racoon[3743] Connecting.
10/28/09 1:23:06 PM racoon[3743] IKE Packet: transmit success. (Initiator, Aggressive-Mode message 1).
10/28/09 1:23:06 PM racoon[3743] IKEv1 Phase1 AUTH: failed. (Initiator, Aggressive-Mode Message 2).
10/28/09 1:23:06 PM racoon[3743] IKE Packet: transmit success. (Information message).
10/28/09 1:23:06 PM racoon[3743] IKEv1 Information-Notice: transmit success. (ISAKMP-SA).
10/28/09 1:23:06 PM racoon[3743] IKE Packet: receive failed. (Initiator, Aggressive-Mode Message 2).

I've been struggling with this issue for months now, and it's gotten particularly bad as of the 10.6.5 upgrade: the Cisco VPN client now causes a kernel panic for me daily!

Finally, out of frustration, I dug into the OSX source and fixed the issue myself.

You can find the fix here:
darwin-racoon-cisco-cert-fix on GitHub

Cheers!