What I must change to make this code listen on UDP port?

Question

I'm trying to create a server Windows Form application but my code throw a 0x80004005 error when call the Listen method. What I'm doing wrong?

Private Sub StartUdpReceiveThread(ByVal Puerto As Integer)
    If Not UdpOpen Then
        Try
           permission = New SocketPermission(NetworkAccess.Accept, TransportType.Udp, "", SocketPermission.AllPorts)

            sListener = Nothing

            permission.Demand()

            'Dim ipHost As IPHostEntry = Dns.GetHostEntry("")

            Dim ipAddr As IPAddress =  IPAddress.Any

            ipEndPoint = New IPEndPoint(ipAddr, CInt(Me.PuertoEscuchaLbl.Text))

            'sListener = New Socket(ipAddr.AddressFamily, SocketType.Unknown, ProtocolType.Udp)
            sListener = New Socket(ipAddr.AddressFamily, SocketType.Dgram, ProtocolType.UDP)

            ' Associates a Socket with a local endpoint 
            sListener.Bind(ipEndPoint)

            sListener.Listen(5)

            ' Begins an asynchronous operation to accept an attempt 
            Dim aCallback As New AsyncCallback(AddressOf AcceptCallback)
            sListener.BeginAccept(aCallback, sListener)

            PrintLog("Server listening on " & ipEndPoint.Address.ToString & " port: " & ipEndPoint.Port)

            UdpOpen = True
        Catch ex As Exception
            MessageBox.Show(ex.ToString())
        End Try
    End If
End Sub

Edit: CallBack method Public Sub AcceptCallback(ar As IAsyncResult) Dim listener As Socket = Nothing

    ' A new Socket to handle remote host communication 
    Dim handler As Socket = Nothing
    Try
        ' Receiving byte array 
        Dim buffer As Byte() = New Byte(1023) {}
        ' Get Listening Socket object 
        listener = DirectCast(ar.AsyncState, Socket)'<-- Here raises an error
        ' Create a new socket 
        handler = listener.EndAccept(ar)

        handler.NoDelay = False

        ' Creates one object array for passing data 
        Dim obj As Object() = New Object(1) {}
        obj(0) = buffer
        obj(1) = handler

        handler.BeginReceive(buffer, 0, buffer.Length, SocketFlags.None, New AsyncCallback(AddressOf ReceiveCallback), obj)

        ' Begins an asynchronous operation to accept an attempt 
        Dim aCallback As New AsyncCallback(AddressOf AcceptCallback)
        listener.BeginAccept(aCallback, listener)
    Catch ex As Exception
        MessageBox.Show(ex.ToString())
    End Try
End Sub

Answer 1

Don't just pick the first IP address in IPHostEntry.AddressList but search the array for an IPv4 address. See the example on this MSDN page .