HttpWebRequest POST Error : webexception was unhandled VB.NET

Dim Username = txt_value.Text
        Dim PostData = "account=" & Username
        Dim request As WebRequest = WebRequest.Create("http://127.0.0.1/post.php")

        request.Method = "POST"
        Dim byteArray As Byte() = Encoding.UTF8.GetBytes(PostData)
        request.ContentType = "application/x-www-form-urlencoded"
        request.ContentLength = byteArray.Length
        Dim dataStream As Stream = request.GetRequestStream()
        dataStream.Write(byteArray, 0, byteArray.Length)
        dataStream.Close()
        Dim response As WebResponse = request.GetResponse()
        dataStream = response.GetResponseStream()
        Dim reader As New StreamReader(dataStream)
        Dim responseFromServer As String = reader.ReadToEnd()
        reader.Close()
        dataStream.Close()
        response.Close()
        MsgBox(responseFromServer)