F17 gnome fallback taskbar panel stopped working

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http://forums.fedoraforum.org – Hi I have a strange problem with the taskbar panel in gnome. It has stopped working completely. When I open a program it does not display in the taskbar (bar at the bottom which shows which programs are open). As a result the only way I can switch between programs/windows is to ALT+TAB. The task bar is there and the auto/hide works as normal but it is just empty, programs are not added to it when I open them. It used to happen from time to time for the past few months but now it does not work as soon as I login. I have not messed with any config files and I have installed all the up (HowTos)