Re-add the default leading panel
See this post. It will certainly recover your panels back to their defaults. It does not differentiate because any kind of edits to your lower panel will certainly additionally be shed.
Open an incurable session by :
pushing Alt F2 > after that type
gnome-terminal > click Run
Then enter the adhering to code :
gconftool-2 –-recursive-unset /apps/panel # might be optional rm -rf ~/.gconf/apps/panel pkill gnome-panel
Edit : Updated for gconftool - 2