VPN (racoon) disappears

Once upon a time, my VPN was happy. It would connect each and every time. Then, I recently added a new connection to a new company's VPN. I began having problems when using one, then switching to the other. I get an error "A configuration error occurred. Verify your settings and try reconnecting." The only way to get it to connect to either target was to manually kill the racoon process (sudo kill proc-id) and restart it (sudo /usr/sbin/racoon).

Sometimes that doesn't work either. I'm seeing that racoon disappears from the process list after I've successfully connected and disconnected to one of the VPN targets. Sometimes I can just start it again, and sometimes I have to repeatedly start, kill, start, kill, etc., before it works again. In the worst cases, I have to reboot. It's quite maddening. I'm not getting any console messages when racoon disappears (I assume crashes, but wouldn't that be in the log?)

Any thoughts? I'm running 10.6.8.