Specified Cast Type not Valid Error C# please help

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C#

I am trying to insert some values into a chart from a database. the first column (X axis) is a String type and the second column ( Y Axis) is float type. I keep getting this error "Cast Type not valid"when ever i press the button. Please help

private void ViewGraphBtn_Click(object sender, EventArgs e)
  {
      try
      {
          Query = "SELECT *  FROM Products;";
          Reader = conn.ExecuteStatement(Query);

          while (Reader.Read())
          {
              this.chart1.Series["Series1"]
                         .Points.AddXY(Reader.GetString(1), Reader.GetInt64(4));
          }
      }
      catch (Exception ex)
      {
           MessageBox.Show(ex.Message);
      }