[Solved] jQuery DataTable Error: Error: System.NullReferenceException: Object reference not set to an instance of an object

Error: System.NullReferenceException: Object reference not set to an instance of an object

Please help me fix it. 

protected void Inkview_Click(object sender, EventArgs e)
{
    gvDetails.UseAccessibleHeader = true;
    gvDetails.HeaderRow.TableSection = TableRowSection.TableHeader;
    int rowIndex = ((sender as Button).NamingContainer as GridViewRow).RowIndex;
    int lbl1 = Convert.ToInt32(gvDetails.DataKeys[rowIndex].Values[0]);
    SqlConnection con = new SqlConnection("data source=NERE\\SQLEXPRESS01; Initial Catalog=kaging;Integrated Security=True;");
    SqlCommand cm = new SqlCommand();
    cm.Connection = con;
    con.Open();
    cm.CommandType = CommandType.Text;
    cm.CommandText = "SELECT productcodeM FROM orders WHERE id= ' " + lbl1 + "' ";
 
    Session["r"] = Convert.ToString(cm.ExecuteScalar());
    updateSQL = "update stock set active='0' where ppid='" + Session["r"].ToString() + "'";
 
    dbConn.ConnectionString = "data source=NERE\\SQLEXPRESS01; Initial Catalog=kaging;Integrated Security=True;";
    cmd.Connection = dbConn;
    cmd.CommandText = updateSQL;
    cmd.CommandType = CommandType.Text;
    try
    { 
        dbConn.Open();
        int updated = cmd.ExecuteNonQuery();
        if (updated == 1)
        { 
             // Response.Redirect("Cylin.aspx");
        }
        else
        {
             // Label1.Text = "Process not Completed";
        } 
    }
    catch (Exception err)
    {
        Response.Write(err.ToString());
    }
    finally
    {
        dbConn.Close();
    }
    BindUserDetails();
    con.Close(); 
    Response.Redirect("UseableCyl.aspx"); 
}