DropDownList not working

The case is .... dropdownlist2 contains 4 values(a,b,c,d)..... and i make them display in page whatever the item is selected ..... if c is selected .... always it selects 'a'... i couldn't get the values of b,c,d ....

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;
using System.Data;

public partial class WebFormAdmin_SelectNetwork : System.Web.UI.Page
{
WorkspaceBAL objBAL = new WorkspaceBAL();
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
select_people.Visible = false;

_LoadNetwkHdList();
display.Visible = false;
}
}


//Bind the Network Header List
void _LoadNetwkHdList()
{
DataTable dt = new DataTable();
dt = objBAL.GetNetwkList("SelectNetwork");
DropDownList1.DataSource = dt;
DropDownList1.DataTextField = "NetwkName";
DropDownList1.DataValueField = "NetwkID";
DropDownList1.DataBind();
DropDownList1.Items.Insert(0, new ListItem("Select", "0"));
}


protected void DropDownList1_SelectedIndexChanged(object sender, EventArgs e)
{
select_people.Visible = true;
int ss = Convert.ToInt32(DropDownList1.SelectedValue);
// _BindEmployeelistByNetwkID(Convert.ToInt32(ddlNetwkName.SelectedValue));
DropDownList2.DataSource = objBAL.GetNetWorkDetailslist(Convert.ToInt32(Session["UserId"]), Convert.ToInt32(ss));
DropDownList2.DataTextField = "EmployeeName";
DropDownList2.DataValueField = "NetwkID";
DropDownList2.DataBind();
DropDownList2.Items.Insert(0, new ListItem("Select", "0"));
}

protected void DropDownList2_SelectedIndexChanged(object sender, EventArgs e)
{
display.Visible = true;
Name.Text = DropDownList2.SelectedItem.Text;

}

}