NAT Error with Shorewall + Linux 2.6.20 on Debian

I just compiled a fresh kernel 2.6.20 under Debian 4.0 (etch), using the same config (working) that I previously used for 2.6.19.2. After booting into the new kernel, shorewall fails to start with the error:

ERROR: Rule "DNAT net loc:192.168.1.100 tcp ##" requires NAT which is disabled

The port number I was forwarding was replaced with "##" for our purposes here.
I double checked the kernel config to make sure that iptables was enabled, and it is.
Does anybody have any ideas? I can't seem to find anything helpful on Google or anywhere else.
Thanks in advance.

Is CONFIG_IP_NF_NAT set?
Is the module loaded? (iptable_nat)

NAT handling has changed for the 2.6.20. I haven't look deeply but nf_conntrack is the module that now takes care of NAT. ip_conntrack will be removed in 2.6.22, this is a major modification.
Try to search on kerneltrap or other kernel/network dev related mailinglist because a lot of people are in your case.
Also probably that iptables must be updated to take into account the modifications. Tools like firestarter do not work properly on 2.6.20 from what I see here.
The easiest is to revert to 2.6.19.x.

I have currently disabled the iptables user space tools because of this modifications (some of my rules also broke) and I don't have currently the time to investigate. I still think that backward compatibily should work so probably your kernel configuration is buggy.
If you find any information, I (and I'm sure a lot of others) would be interested.

Yeah, it was my kernel config that was the problem. Going from 2.6.19.2 to 2.6.20, they essentially changed the location of NAT. By doing a 'make oldconfig', I was able to select what they're now calling "Full NAT", and then all the modules were properly built.
Everything seems to be working as it should now. I haven't tried virtualization in the new kernel, since I have no use for it on a server, but I can say that the boot time is much faster.
Thanks for the suggestions.

spindley, I didn't understand if you manage to get NAT working on 2.6.20 or returned to 19?