เกิดปัญหาโค้ดปุ่มดาวโหลดช่วยทีครับ asp.net vb - 0x800a1391 - JavaScript runtime error: 'DownloadFile' is undefined

 Protected Sub DownloadFile(sender As Object, e As EventArgs)

        Dim id As Integer = Integer.Parse(TryCast(sender, LinkButton).CommandArgument)
        Dim bytes As Byte()
        Dim fileName, contentType As String
        Dim constr As String = "Server=ADMIN;UID=sa;PASSWORD=1234;database=xxx;Max Pool Size=400;Connect Timeout=600;"
        Using con As New SqlConnection(constr)
            Using cmd As New SqlCommand()
                cmd.CommandText = "SELECT * FROM fileonwebboard WHERE FilesID=@FilesID"
                cmd.Parameters.AddWithValue("@FilesID", id)
                cmd.Connection = con
                con.Open()
                Using sdr As SqlDataReader = cmd.ExecuteReader()
                    sdr.Read()
                    bytes = DirectCast(sdr("FilesName"), Byte())
                    contentType = sdr("FilesType").ToString()
                    fileName = sdr("Name").ToString()
                End Using
                con.Close()
            End Using
        End Using
        Response.Clear()
        Response.Buffer = True
        Response.Charset = ""
        Response.Cache.SetCacheability(HttpCacheability.NoCache)
        Response.ContentType = contentType
        Response.AppendHeader("Content-Disposition", "attachment; filename=" + fileName)
        Response.BinaryWrite(bytes)
        Response.Flush()
        Response.End()

    End Sub