[ubuntu_studio] Top XFCE panel (taskbar) stops working

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http://ubuntuforums.org – I'm having problems with the XFCE top panel in Ubuntu Studio 12.04. Several times a day when I click on the open tabs, nothing happens and the right hand side log out/shut down menu also is gone. I have to do a hard reboot. Rebooting restores the panel. I've just been investigating the Panel Preferences and see that there are two panels. I have just deleted one of them so I now have just the one. Any suggestion gratefully received (Hardware)