how do I diagnose "unable to handle kernel paging request"

[straits at cts.com]

I got a message saying "unable to handle kernel paging request"
along with an Oops:0002 when starting
emacs and again later when shutdown tried to unmount filesystems.
The message also gave contents of some registers and the stack
and gave a call trace in hex.

A reboot may have fixed the problem, at least for the moment.
I have a stock kernel.  What is likely to be wrong?  What information
should I post to help diagnose?  Where might I look online for
extra information?

Thanks very much.