[VB2010] Submit form con web client

[Skyscraper84]

Ciao,
dovrei effettuare il submit di un form utilizzando un web client.
ho provato il seguente codice

Dim web As New System.Net.WebClient()
  
Public Sub Prova()
        Try
            web.Headers.Add("Content-Type", "application/x-www-form-urlencoded")
            Dim d As Byte() = System.Text.Encoding.ASCII.GetBytes("username=" & Utente & "&password=" & Password)
            Dim res As Byte() = web.UploadData(https://urlaction, "POST", d)
            Dim s As String
            s = System.Text.Encoding.ASCII.GetString(res)
            Console.WriteLine(s)
        Catch ex As Exception
            Debug.Print(ex.Message)
        End Try
       End Sub

oppure

Dim WebClient As New WebClient()
   
Public Sub Authenticate(username As String, password As String)
        Dim data As New NameValueCollection()
 
        data.Add("username", username)
        data.Add("password", password)
 
        Dim res As Byte() = WebClient.UploadValues(("https://urlaction"), data)
        Dim s As String
        s = System.Text.Encoding.ASCII.GetString(res)
        Console.WriteLine(s)
       End Sub

ma mi stampa sulla console il codice HTML della pagina come se facessi il submit senza indicare nessun valore.

Dove sbaglio?