ASP.NET

hi - i'm working on an asp.net page that has a DDL and depending on the DDL selection will display a gridview of results. Here's the code I have so far:

Code:
<%@ Page Title="GDNI_SalesmanManager" Language="C#" MasterPageFile="~/Site.master" AutoEventWireup="true"
    CodeBehind="GDNI_SalesmanManager.aspx.cs" Inherits="GDNI_Salesman_Manager.About" %>

<asp:Content ID="HeaderContent" runat="server" ContentPlaceHolderID="HeadContent">
    <style type="text/css">
        .style1
        {
            width: 251px;
            height: 120px;
        }
    </style>
</asp:Content>
<asp:Content ID="BodyContent" runat="server" ContentPlaceHolderID="MainContent">
    <h2>
        Customer:
        <asp:DropDownList ID="ddlCustomers" runat="server" Height="17px"
            ToolTip="Customers" Width="285px">
        </asp:DropDownList>
    </h2>
    <p>
        &nbsp;<asp:GridView ID="gvProductClass" runat="server">
        </asp:GridView>
    </p>
</asp:Content>


<pre lang="c#">
using System;
using System.Data;
using System.Configuration;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data.SqlClient;


namespace GDNI_Salesman_Manager
{
    public partial class About : System.Web.UI.Page
    {
        string strConnString = ConfigurationManager.ConnectionStrings["BB_Datawarehouse_DB"].ConnectionString;
        string str;
        SqlCommand com;

        protected void Page_Load(object sender, EventArgs e)
        {
            ddlCustomers.AutoPostBack = true;

            if (!IsPostBack)
            Populate_ddlCustomers();
        } //in debug mode the code skips to site.master page load event


        public void Populate_ddlCustomers()
        {
            ddlCustomers.Items.Add("Please Select a Customer");
            SqlConnection con = new SqlConnection(strConnString);
            con.Open();
            str = "exec dbo.sp_GetCustNumAndDSeq";
            com = new SqlCommand(str, con);
            SqlDataReader reader = com.ExecuteReader();
            while (reader.Read())
            {
                ddlCustomers.Items.Add(reader["Customer"].ToString());
            }
            reader.Close();
            reader.Dispose();
        }

        protected void ddlCustomers_SelectedIndexChanged(object sender, EventArgs e)
        {
            SqlConnection con = new SqlConnection(strConnString);
            con.Open();
            str = "exec dbo.sp_GetProductClsCodeAndSalesman '" + ddlCustomers.SelectedItem.Text + "'";
            com = new SqlCommand(str, con);
            SqlDataReader reader = com.ExecuteReader();
            while (reader.Read())
            {
                gvProductClass.DataSource = reader;
                gvProductClass.DataBind();
            }
            reader.Close();
            con.Close();
        }
    }
}

Sir.. I have two pages in websites.  I have a label and button on first  page, for 'Postbackurl ' property of button of first page ,I have taken url of second page.. & I have taken another label on second page I have added  ..
<System.Web>
<sessionState Timeout="1"/>
</System.Web>   into web.config file

so when i run the page ..first page will be opened ..then after 1 min I clicked on button still second page successfully opened.

and I want show by using label that..." Session is expired ".

Thanks & Regards
-Rakesh

<asp:LinkButton ID="LinkButton7" runat="server"
  CommandArgument="nl" OnClick="RequestLanguageChange_Click" class="flagbutton">
  <asp:Image ID="Image1" runat="server" ImageUrl="~/images/flagnl.png" tooltip="Bekijk deze website in het Nederlands" title="Bekijk deze website in het Nederlands"/>
  <img class="map" src="images/flaghovernl.png" alt=""/>
  </asp:LinkButton>

<a href="about.aspx?lang=nl">Nederelands</a>