Modules suddenly missing

[Graham Williams <Graham.Williams@cmis.CSIRO.AU>]

About a week ago I updated a Debian box, running a custom kernel
2.4.16, with a dist-upgrade in unstable (it's been running unstable
for a long time, and this just brought it up to date).

On the next reboot (a few days later) things started breaking! In
particular nfs, audio, and cdrom and cdrw access.  I think I've
tracked the problems to the appropriate kernel modules not being
loaded? Why would a dist-upgrade cause this? I can add nfs, and nfsd
to /etc/modules and NFS is working again. I can add i810_audio and
audio is up agian. Also isofs, ide-cd, ide-probe-disk, and ide-disk
get CDROM going again.  I've failed so far to get the CD-RW working
again:

# mount /cdrw
mount: /dev/scd0 is not a valid block device

My questions: 

   What could have changed to the modules stuff to cause these to no
   longer be loaded on boot?

   Any ideas on why my ide-scsi CD-RW set up would be failing.  A
   scanbus does not find the ide-scsi CD-RW.

Thanks
Graham

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