L2TP Problem with CISCO

[Edge]

Good morning everyone.
Today i've tried to set up an L2TP Tunnel between my Pfsense and a foreign CISCO Router. Note: Only L2TP without IPSec!
I've created the L2TP Server as described at the Pfsense doc's section. (Set an IP Adress, unused by Firewall, added a remote Client subnet, pasted my secret Password, authentication type PAP and let everything else unchanged)
Then i created the Firewallrules (L2TP Tab allow any to any on all Ports; wan tab allow 1701 UDP from any)
Now i can see the CISCO Box connecting, but i get immediatly the following:

Jun 2 14:16:26 l2tps: L2TP: Control connection 0x803462308 destroyed
Jun 2 14:16:15 l2tps: L2TP: Control connection 0x803462308 terminated: 0 ()
Jun 2 14:16:15 l2tps: Incoming L2TP packet from 1.2.3.4 1701

My tcpdump on the WAN Interface looks like this:

IP 5.6.7.8.1701 > 1.2.3.4.1701:  l2tp:TLSNs=0,Nr=1 *MSGTYPE(StopCCN) *ASSND_TUN_ID(61512) *RESULT_CODE(4/0)
14:21:22.026952 IP 1.2.3.4.1701 > 5.6.7.8.1701:  l2tp:TLSNs=1,Nr=1 ZLB
14:22:37.009611 IP 1.2.3.4.1701 > 5.6.7.8.1701:  l2tp:TLSNs=0,Nr=0 *MSGTYPE(SCCRQ) *PROTO_VER(1.0) FIRM_VER(4400) *HOST_NAME(vcdsl2) VENDOR_NAME(Cisco Systems, Inc.) *RECV_WIN_SIZE(20050) *CHALLENGE(fhuezfgg62g83e34d3e0162) *ASSND_TUN_ID(65256) *FRAMING_CAP() *BEARER_CAP() VENDOR0009:ATTR006e()

Of course i changed the IP Adresses and the challenge request.
Could someone point me to the right direction please? I think i am missing something, but dunno what.

Thanks in advance
Edge

[Edge]

Anyone?
I'm still trying to get this things working….
Thank you!