On reselecting the dropdown box the listbox values are not changing .

protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
DataManager myData = new DataManager(DbFunctions.GetConnectionString());
MySqlConnection myPConn = myData.GetPooledConnection(new MySqlConnection());
MySqlCommand cmd = new MySqlCommand("SELECT adminuserid,adminusername FROM adminusermast ", myPConn);
DataTable dt = new DataTable();
myPConn.Open();
MySqlDataAdapter adptr = new MySqlDataAdapter(cmd);
adptr.Fill(dt);
myPConn.Close();
if (dt.Rows.Count > 0)
{
ddlAdmin.Items.Clear();
ddlAdmin.Items.Add("SELECT");
foreach (DataRow drow in dt.Rows)
{
ListItem lst = new ListItem();
lst.Value = drow[0].ToString();
lst.Text = drow[1].ToString();
ddlAdmin.Items.Add(lst);
}
}
}
}


protected void FillProductList()
{

DataManager myData = new DataManager(DbFunctions.GetConnectionString());
MySqlConnection myPConn = myData.GetPooledConnection(new MySqlConnection());
MySqlCommand com = new MySqlCommand("select * from productmast where productid NOT IN (select productid from userpermission where adminuserid =" + ddlAdmin.SelectedIndex.ToString() + ")", myPConn);
MySqlDataReader Reader = null;
myPConn.Open();
Reader = com.ExecuteReader();
while (Reader.Read())
{
ListItem newItem = new ListItem();
newItem.Text = Reader["productname"].ToString();
newItem.Value = Reader["productid"].ToString();
ProductListBox.Items.Add(newItem);
}
Reader.Close();
myPConn.Close();
}

protected void FillProuductPermissionList()
{
DataManager myData = new DataManager(DbFunctions.GetConnectionString());
MySqlConnection myPConn = myData.GetPooledConnection(new MySqlConnection());
MySqlCommand com = new MySqlCommand("select * from userpermission u inner join productmast p on u.productid = p.productid where adminuserid =" + ddlAdmin.SelectedIndex.ToString() + "", myPConn);
MySqlDataReader Reader = null;
myPConn.Open();
Reader = com.ExecuteReader();
while (Reader.Read())
{
ListItem newItem = new ListItem();
newItem.Text = Reader["productname"].ToString();
newItem.Value = Reader["productid"].ToString();
PermissionListBox.Items.Add(newItem);
}
Reader.Close();
myPConn.Close();
Response.Write(ddlAdmin.SelectedIndex.ToString());
}
protected void AdminDropDown_Selected(object sender, EventArgs e)
{
FillProductList();
ProductListBox.Visible = true;
BtnMoveLeft.Visible = true;
ButtonMoveRight.Visible = true;
PermissionListBox.Visible = true;
FillProuductPermissionList();
}
protected void BtnMoveleft_Click(object sender, EventArgs e)
{
if (ProductListBox.SelectedIndex == -1)
{
LabelError.InnerHtml = "No Data Selected";
}
for (int i = ProductListBox.Items.Count - 1; i >= 0; i--)
{
if (ProductListBox.Items[i].Selected == true)
{
PermissionListBox.Items.Add(ProductListBox.Items[i]);
ListItem li = ProductListBox.Items[i];
ProductListBox.Items.Remove(li);
}
}
BtnPermission.Enabled = true;

}
protected void Permission_Accepted(object sender, EventArgs e)
{
DataManager myData = new DataManager(DbFunctions.GetConnectionString());
MySqlConnection myPConn = myData.GetPooledConnection(new MySqlConnection());
for(int i=PermissionListBox.Items.Count-1;i>=0;i--)
{