Explorer not pinned to taskbar in Windows 7 beta

Hi,
I somehow got windows explorer unpinned from the taskbar when explorer froze on me. Now I can not pin it back. When I try to drag the shortcut on the start menu it always shows a unavailable circle. When i go to the windows folder and right click on explorer.exe, I see pin to taskbar and pin to start menu. when I selecte pin to start menu it is pinned, but when i select pin to taskbar nothing happens. Is this some kind of bug?

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Stuart