[Openswan Users] Troubleshooting ipsec/l2tp

[klas]

I've got two machines in the same LAN. Both have (as far as I can tell)
identical configurations for ipsec and xl2tpd. Once machine can connect
as client to the server, the other one can't.
The clients and the server are both behind NAT.

ipsec seems to come up fine for both machines, but machine 2 is not
able to set up l2tp. It's sending one packet and gets no answer.

Any pointers about how to troubleshoot this?

Thanks
Klas