kernel panic on or after bootup

I have four pcs running NetBSD 3.0. On reboot I'm regularly seeing a
kernel panic from three of them, either during bootup of within a few
minutes later. The pc that doesn't seem to show the problem is a p4-
2000, whilst slowest an amd586-133 is most likely to give the panic,
maybe 1 in 3 reboots. The k6-400 has managed uptime of 41 days and
then had to be rebooted a couple of times to use a new kernel. I've
seen the problem with GENERIC kernel but needed some extra options
and took the oportunity to remove others that weren't relevant.

Error is same:
kernel: page fault trap, code=0
Stopped at: netbsd:fr_derefrule+0x1c7: cmpl $0x2,0x88(%edx)

Any ideas as to how to track this down?


David