oops in 2.6.38, possibly nf_conntrak_ipv4 related

Hello.

I just upgraded from ubuntu 10.10 (2.6.35) to 11.04 (2.6.38) on an amd64 
machine.

2.6.38-11-generic #50-Ubuntu SMP Mon Sep 12 21:17:25 UTC 2011 x86_64 x86_64 x86_64 GNU/Linux

About 12-14 hours after reboot, the machine oopsed and went offline. I 
took a picture of the trace which can be found here:

<http://swm.pp.se/IMG_0937.JPG>

To me, it looks like something went wrong in nf_conntrak_ipv4, but I am 
quite the novice regarding this.

I did not have any NAT rules enabled, the only iptables that is enabled 
are some simple port blocks with "-j REJECT --reject-with tcp-reset" for 
the world with a few exceptions (my own networks).

Any ideas? If this is the wrong place to turn to, pointers on where to go 
is much appreciated.

-- 
Mikael Abrahamsson    email: swmike@swm.pp.se