Salve a tutti, qualcuno mi saprebbe dire perche questo codice mi restituisce valori sbagliati?

codice:
Dim PostData As String = "username=" & TextBoxX1.Text & "&password=" & TextBoxX2.Text & "&return=aW5kZXgucGhwP29wdGlvbj1jb21fdXNlcnMmdmlldz1wcm9maWxl&eaf3f5cf5a5d7fec88d3c00e013b3a3e=1"
        Dim TempCookies As New CookieContainer
        Dim Encoding As New UTF8Encoding
        Dim ByData As Byte() = Encoding.GetBytes(PostData)


        Dim PostReq As HttpWebRequest = DirectCast(WebRequest.Create("http://www.ironnetwork.altervista.org/index.php?option=com_users&view=login"), HttpWebRequest)
        PostReq.Method = "POST"
        PostReq.KeepAlive = True
        PostReq.CookieContainer = TempCookies
        PostReq.ContentType = "application/x-www-form-urlencoded"
        PostReq.Referer = "http://www.ironnetwork.altervista.org/"
        PostReq.UserAgent = "Mozilla/5.0 (Windows NT 6.1; WOW64; rv:23.0) Gecko/20100101 Firefox/23.0"
        PostReq.ContentLength = ByData.Length


        Dim postreqstream As Stream = PostReq.GetRequestStream
        postreqstream.Write(ByData, 0, ByData.Length)
        postreqstream.Close()
        Dim postresponse As HttpWebResponse


        postresponse = DirectCast(PostReq.GetResponse(), HttpWebResponse)
        TempCookies.Add(postresponse.Cookies)
        Dim postreqreader As New StreamReader(postresponse.GetResponseStream())


        Dim Page As String = postreqreader.ReadToEnd


        If Page.Contains("coincidono") Then
            MsgBox("Login Failed")
        Else
            MsgBox("Login succesfull")
        End If
Per valori sbagliati, intendo che mi da o sempre succesful o sempre failed :c