What happens if you NOW run:
Does it start ? .. if so, you need to edit the command
for the hp-systray item in startup applications from:-
sh -c "sleep 15; exec hp-systray"
It seems like hp-systray is attempting to start before the system tray is loaded .. changing that command will introduce a 15 second delay in starting hp-systray, giving the system tray time to come up first.
If you're not sure how to change the hp-systray startup applications command line .. ask.