ipfw: getsockopt(IP_FW_ADD): Invalid argument

[Unga]

Hi all

Following ipfw rule develop error indicated in the subject line:
ipfw add 100 fwd 127.0.0.1,1234 tcp from any to any 1234 out via wlan0

What I want to do is forward any packet going to port 1234 to 127.0.0.1:1234.

I have built the kernel with "options         IPFIREWALL_FORWARD".

What's the error here? Is the rule incorrect?

This is FreeBSD 8.1.

Many thanks in advance.

Unga