Close preview windows or not can lead to error :
[2013-01-13 16:21:24,109] [69794 ] [SetupTv ] [Mediaportal.TV.Server.TVLibrary.Integration.MP1.Logger] [ERROR] - Exception in setuptv
System.NullReferenceException: Object reference not set to an instance of an object.
   at Mediaportal.TV.Server.SetupTV.Dialogs.FormPreview.ShowDialog(IWin32Window owner)
   at Mediaportal.TV.Server.SetupTV.Sections.ChannelsInGroupControl.mpButtonPreview_Click(Object sender, EventArgs e)
   at System.Windows.Forms.Control.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnClick(EventArgs e)
   at System.Windows.Forms.Button.OnMouseUp(MouseEventArgs mevent)
   at System.Windows.Forms.Control.WmMouseUp(Message& m, MouseButtons button, Int32 clicks)
   at System.Windows.Forms.Control.WndProc(Message& m)
   at System.Windows.Forms.ButtonBase.WndProc(Message& m)
   at System.Windows.Forms.Button.WndProc(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.OnMessage(Message& m)
   at System.Windows.Forms.Control.ControlNativeWindow.WndProc(Message& m)
   at System.Windows.Forms.NativeWindow.Callback(IntPtr hWnd, Int32 msg, IntPtr wparam, IntPtr lparam)