Automatic updates sometimes don't work

I have 6 windows 2003 enterprise servers all set to perform automatic
updates. I have it set to automatically download and install the updates.

I have noticed that the update process does not always work. This last
windows security update in the past few days did not automatically update,
and I had no indication that there was even an update to install. I had to
browse to the windowsupdate site and install them manually on all my servers.

This lattest update required a re-boot, that is the only thing I see
different than the other updates that have worked in the past. Not sure if
that's the reason, but if so I would think auto update would at least notify
me that the update is available by placing the update icon in my tray.

Any ideas on this one.

Paul