Spontaneous SIGTERM

[Robert E. Butts]

My apologies if this message shows up twice.  I submitted it once with
the wrong email address (mine), and the bot bounced it.  Trying again,
with the correct email address:

I have Ubuntu 6.06 installed on two of my PC's.  On one of the two,
about once every other day, and usually at night when the PC is idle,
the kernel executes a spontaneous SIGTERM (Signal 15) and ends my
session.  When I get up and check the computer, I see a login screen,
not my desktop.  

This would not be an issue, normally, but one of the things I use this
PC for is an alarm clock to remind me to take me medicine, and to wake
me in the morning.  If I'm not logged in those reminders don't run, and
that's a problem I cannot live with.  They have to run.  

Any thoughts about why I'm being logged out of my session, and what I
can do about it?

TIA