PfSense 2.0.1 <-> Fritz!Box Fon WLAN 7270, IPsec

[tps800]

Hi!

I've managed to set up an IPsec tunnel between a Fritz!Box and pfSense.
After setting it up all was fine. For hours it worked. But now: the tunnel in question is shown as active on both sides: the Fritz!Box and pfSense. Trying to ping a printer on the other side fails. The printer is at sleep, but it answers to icmp echo requests.
Vice versa the same: from a PC on the remote side I can't ping anything running and up localy. Really bad.

After restarting pfSense and Fritz!Box it works again. Until the next line interruption by the provider.

Within the logs I find on Fritz!Box and pfSense the same: only messages stating the connection is established. But no data crosses the wire!

My setup is:
PC1 (192.168.6.22) <-> (192.168.6.1/24) Fritz!Box (DSL)
  <-> Internet <->
  (fixed address) pfSense (192.168.180.27/23) <-> (192.168.180.4) PC2

Routes on both PC are set to take Fritz!Box or pfSense as router for any subnet 192.168.0.0/16. A default route is set for the local internet connection router:

PC1:
defaultroute: 192.168.6.1
route: 192.168.0.0/16 gw 192.168.6.1

PC2:
defaultroute: 192.168.180.1
route: 192.168.0.0/16 gw 192.168.180.27

Now trying to ping from PC1 to PC2 or vice versa:

PC2$ ping 192.168.6.22
PING 192.168.6.22 (192.168.6.22) 56(84) bytes of data.
^C
–- 192.168.6.22 ping statistics ---
588 packets transmitted, 0 received, 100% packet loss, time 587008ms

Any idea?