Date:        Mon, 7 Jul 2003 16:53:12 -0700 (PDT)
    From:        Dobromir Montauk <dmontauk@rescomp.berkeley.edu>
    Message-ID:  <Pine.LNX.4.50.0307071648070.26584-100000@hal.rescomp.berkeley.edu>

  | We've deployed NetBSD 1.6 on half a dozen servers.  We have the kernel
  | compiled with all the ALTQ & IPSEC tags enabled on half the servers - the
  | other half don't have ALTQ.

Are you sure the ALTQ enabled kernel is a 1.6 kernel, and not -current ?
What does uname -r report about it ?   (and the other one).

If you were running a -current kernel sometimes, and a 1.6 (or 1.6.1)
kernel at other times, all this would be explained - -current updates
some of the super block fields differently than 1.6[.1] fsck expects.
You need fsck sources from -current as well (but compiled under 1.6)
to be able to switch back and forth between those two kernels.

If this is the problem, there most likely is no real file system
corruption, just the appearance of it.

kre