Slide Effect Presentation Creator Released

I got an error when tried to delete some effects (Delete selected object button->sample.sef->slide 2):

Object reference not set to an instance of an object.
Stack Trace:
at SlideEffect.tabs.main.Tab.OnRemoveObject(SEObjectDisplay o)
at SlideEffect.tabs.main.SlideDisplayCtrl.SESlideViewContainer.OnObjectDelete(SEObjectDisplay o)
at SlideEffect.tabs.main.SlideDisplayCtrl.SESlideViewContainer.deleteButton_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)