lost panel icons

[emilemma]

i added several icons to my bottom panel using the 'add to panel' feature. they were all launchers for firefox to various websites. locked icons to panel and all was fine... until i reboot or restart ubuntu 10.04. then some of the icons did not show and some did. later when restarting they reappeared. this happens off & on. any ideas??
this is a gnome desktop.

i am new to ubuntu and linux.

thanks :D