We are not getting TeeChart's Paint Event on Runtime. For other controls Paint event is getting called successfully. AfterDraw event works fine instead. Code to reproduce the problem:

    public Form1()
    {
      InitializeComponent();
      InitializeChart();
    }

    private void InitializeChart()
    {
      var series = new Steema.TeeChart.Styles.Points(tChart1.Chart);
      series.FillSampleValues();

      tChart1.Paint += TChart1_Paint;
      //tChart1.AfterDraw += TChart1_AfterDraw;
      tChart1.MouseMove += TChart1_MouseMove;
    }

    private void TChart1_AfterDraw(object sender, Steema.TeeChart.Drawing.Graphics3D g)
    {
      g.Pen.Color = Color.Red;
      g.Line(new Point(0, MouseLocation.Y), new Point(Width, MouseLocation.Y));
      g.Pen.Color = Color.Black;
      g.Line(new Point(MouseLocation.X, 0), new Point(MouseLocation.X, Height));
    }

    private void TChart1_MouseMove(object sender, MouseEventArgs e)
    {
      MouseLocation = e.Location;
      tChart1.Invalidate(); //or tChart1.Draw();
    }

    Point MouseLocation;

    private void TChart1_Paint(object sender, PaintEventArgs e)
    {
      e.Graphics.DrawLine(Pens.Red, new Point(0, MouseLocation.Y), new Point(Width, MouseLocation.Y));
      e.Graphics.DrawLine(Pens.Black, new Point(MouseLocation.X, 0), new Point(MouseLocation.X, Height));
    }