I was playing with this (just moving my mouse to the right, then the left, then clicking "Show right panel" and "Show left panel" (not very professional bug testing, I know!!) and suddenly, as I moved the mouse to the right, the right panel popped out, displaying the left panel! The error dialogue box came up:
MusicBee v2.1.4750.33373 (Win6.1), 3 Jan 2013 21:27:
System.ObjectDisposedException: Cannot access a disposed object.
Object name: '#=qL_G3lktVw1hmsADdu1evVEIGwenw6ws3nhiRb61V8aAQy8sG95eT59AjNPCUXD$R'.
at System.Windows.Forms.Control.CreateHandle()
at System.Windows.Forms.Form.CreateHandle()
at System.Windows.Forms.Control.get_Handle()
at System.Windows.Forms.Form.Show(IWin32Window owner)
at #=qHYN7LyfXC$K_BG_zw3gJ3msHcF0pYxYFkIGQv8hUDMY=.#=qmRO96eoarfuRhjrHjOkgPQzF1hGTPCX9_n66F0crrfk=(Boolean #=qtS979M8i3vDGeu8jJEzjJg==, #=qRN0PtJ_sEiU$Hap8ss2oATtBZ8rGPdmEU7lu3pWQ9eA= #=q_ERGMkHMHzY9WmVnEAbq4g==)
at #=qHYN7LyfXC$K_BG_zw3gJ3msHcF0pYxYFkIGQv8hUDMY=.#=qvV9PdOuhFP5jHBCr9jk5pEGt$CFh5JleXnTW9RswZFs=(Object #=qlKMaJZ5BatifhqdTcWzdRA==, EventArgs #=qYdOy1UiNrsEYWc9xnK53TQ==)
at System.Windows.Forms.Timer.OnTick(EventArgs e)
at System.Windows.Forms.Timer.TimerNativeWindow.WndProc(Message& m)
at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)
and the next time I moved the mouse to the left, it came up again. Then it was blank. Now every time I move my mouse over, an error box comes up, instead of the panel. Clicking the "Show right panel" button functions normally, and the right panel works then. Restarting MB seems to have fixed this, but I thought you should know anyway. The only thing I did that was different to normal is making the right panel wider (cos its collapsable now :-) )
Hope it's not too tough to fix,
Cheers