The fact remains that although people immediately assume that you can't
handle the little arrow icon that says "Show hidden icons" that Windows XP
does sometimes make icons in the "System Tray" (Notification Area) disappear
with NO EXPLINATION. It seems to happen when an error occurs when loading
the profile, or sometimes when Explorer is forced to re-start after a
critical error and "needs to close". The only way I have found to get them
back is to Log off and Log back ON again. This always has them all back
again for me at any rate.
You say "it seems to happen after an error occurs...".
Well, if that is the case and the icons disappear after the error (or
seems to), then perhaps it is the error itself that somehow made the
icons disappear, maybe just temporarily in your case until you reboot
or login again, which is a pretty serious way to "fix" a problem.
I have never seen an anything just disappear by itself - it is always
preceded by some other event. There is always a "something else" that
happens first. The disappearing icons is not the problem, they are a
symptom of the problem. Fix the problem or fix the symptom (and fix
it again).
Rebooting, login and logout, I imagine reloads and resets a lot of
things. The original problem is still there (whatever brought on the
error), so it will probably happen again as soon as whatever caused it
in the first place is repeated.
Maybe we have just been lucky around my place, but there has always
been an explanation or preceding event. The service quit running
(why), some Explorer crash (why)...
I have seen plenty of people that did not notice the < or the >> on
the Quick Start menu. Wow!
We have not heard from the OP yet. If the icons are not there and the
OP starts poking around in the registry for a solution, then some less
invasive troubleshooting methods should be offered first (IMHO). The
OP problem may just be properties. Maybe something else. We are just
guessing right now.