Gnome panel problem on Ubuntu 13.04

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http://ubuntuforums.org – Hello, I've installed Ubuntu 13.04 on my laptop. I am using the Gnome desktop environment. After installation of gnome-shell, I've checked the desktop and didn't like it. So, I added gnome-fallback-session and got my old and familiar interface with panel at the bottom of the screen as I like. I encountered very strange problem. After rebooting and logging in, the panel disappears. I log out (Ctrl-Alt-Del) and log in back the panel returns. I re-install fallback session, uninstall Unity but the problem still remained unsolved. Any help ..?? Baruch Bahar (Hardware)