Problem connecting from Lion (10.7.2) to VPN on Leopard (10.5.8)

Hi,

I set up a VPN (L2TP over IPSec) server on my eMac running Leopard (not Server that is!). I can confirm it's running and working, since I can connect to the VPN server from my iPhone (connected to the internet via 3G). The problem is: when I try to connect to the VPN using my MacBook Pro running Lion (10.7.2) I am not able to connect.

I tried connecting when I was in the local coffee shop connected to their WiFi, but to no avail. When I try to connect when I'm at home (where the eMac is) I can't seem to connect either.

This is what my logfile looks like, when I try to connect:

Nov 23 00:38:28 Computer-van-xx-2 pppd[73494]: pppd 2.4.2 (Apple version 560.13) started by Jelle, uid 501

Nov 23 00:38:28 Computer-van-xx-2 pppd[73494]: L2TP connecting to server 'xxx.dyndns.org' (xxx.xxx.xxx.xxx)...

Nov 23 00:38:28 Computer-van-xx-2 pppd[73494]: IPSec connection started

Nov 23 00:38:28 Computer-van-xx-2 racoon[73265]: Connecting.

Nov 23 00:38:28 Computer-van-xx-2 racoon[73265]: IPSec Phase1 started (Initiated by me).

Nov 23 00:38:28 Computer-van-xx-2 racoon[73265]: IKE Packet: transmit success. (Initiator, Main-Mode message 1).

Nov 23 00:38:28 Computer-van-xx-2 racoon[73265]: IKE Packet: receive failed. (malformed or unexpected cookie).

Nov 23 00:38:31 Computer-van-xx-2 racoon[73265]: IKE Packet: transmit success. (Phase1 Retransmit).

Nov 23 00:38:31 Computer-van-xx-2 racoon[73265]: IKE Packet: receive failed. (malformed or unexpected cookie).

Nov 23 00:38:34 Computer-van-xx-2 racoon[73265]: IKE Packet: transmit success. (Phase1 Retransmit).

Nov 23 00:38:34 Computer-van-xx-2 racoon[73265]: IKE Packet: receive failed. (malformed or unexpected cookie).

Nov 23 00:38:37 Computer-van-xx-2 racoon[73265]: IKE Packet: transmit success. (Phase1 Retransmit).

Nov 23 00:38:37 Computer-van-xx-2 racoon[73265]: IKE Packet: receive failed. (malformed or unexpected cookie).

Nov 23 00:38:38 Computer-van-xx-2 pppd[73494]: IPSec connection failed

Can someone figure out why it's not working (whether I'm at home or on the road)?

PS:

I checked the portforwarding on my Airport Extreme and on my router, dyndns settings and the firewall settings. Everything is working, since my iPhone can connect.