Hmmm, I never seen that error before. :'( A google search didn't turn up much either, but it does look like it might be a problem with the loopback interface from what I did find.
What does "ifconfig" or "ifconfig -a" show. Without the quotes. I don't remember if the "-a" switch was required for 6.1 or not. It has been a long time since I ran a 6.x box.