พี่ๆๆๆที่รักค่ะช่วยดูโค้ดให้ทีค่ะ .. insert ค่าใน DropDownlist ไม่ได้ค่ะ

Imports System.Data
Imports System.Data.OleDb
Partial Class frm_insert
    Inherits System.Web.UI.Page


    Protected Sub crl_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles crl.Click
        txtbook_id.Text = ""
        txtbook_name.Text = ""
        txtbook_by.Text = ""
        txtbook_number.Text = ""
        txtbook_detail.Text = ""
        txtbook_price.Text = ""
        lblstatus.Text = ""

    End Sub

    Protected Sub save_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles save.Click
        Dim strConn As String
        Dim strSQL As String
        Dim objCmd As New OleDbCommand
        strConn = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Server.MapPath("App_Data/mydatabase.mdb") & ";"

        Dim objCon As New OleDbConnection(strConn)
        objCon.Open()
        strSQL = "INSERT INTO tb_book(book_id,book_name,book_by,book_number,book_detail,book_price,type_id)"
        strSQL &= " VALUES ('" & txtbook_id.Text & "',"
        strSQL &= "'" & txtbook_name.Text & "',"
        strSQL &= "'" & txtbook_by.Text & "',"
        strSQL &= "'" & txtbook_number.Text & "',"
        strSQL &= "'" & txtbook_detail.Text & "',"
        strSQL &= "'" & txtbook_price.Text & "',"
        strSQL &= "'" & Me.listtype_id.SelectedItem.Value & "')"

        With objCmd
            .Connection = objCon
            .CommandText = strSQL
            .CommandType = CommandType.Text
        End With
        Try
            objCmd.ExecuteNonQuery()
            Me.lblstatus.Text = "บันทึกข้อมูลเรียบร้อยแล้ว"
            Me.lblstatus.Visible = True
            Response.Redirect("frm_insert.aspx")
        Catch ex As Exception
            Me.lblstatus.Visible = True
            Me.lblstatus.Text = " ไม่สามารถบันทึกข้อมูลได้(" & ex.Message & ")"
        End Try

    End Sub

    Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
        Dim objCon As OleDbConnection
        Dim dtAdapter As OleDbDataAdapter
        Dim dt As New DataTable

        Dim strCon As String
        strCon = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=" & Server.MapPath("App_Data/mydatabase.mdb") & ";"
        objCon = New OleDbConnection(strCon)
        objCon.Open()

        Dim strSQL As String
        strSQL = "SELECT *FROM tb_type"
        dtAdapter = New OleDbDataAdapter(strSQL, objCon)
        dtAdapter.Fill(dt)
        dtAdapter = Nothing
        objCon.Close()
        objCon = Nothing
        With Me.listtype_id
            .DataSource = dt
            .DataTextField = "type_name"
            .DataValueField = "type_id"
            .DataBind()

        End With
        listtype_id.SelectedIndex = listtype_id.Items.IndexOf(listtype_id.Items.FindByValue("type_id"))
End Sub