[RESOLVED] need help in The underlying connection was closed: Could not establish trust relation

Code:

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Imports System.Net
Imports System.IO
Imports System.Text
Imports System.Security.Cryptography.X509Certificates
Imports System.Net.Security

Public Class Form1
    Dim logincookie As CookieContainer


    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        Dim postdata As String = "username=" & TextBox1.Text & "&password=" & TextBox2.Text & "&sub_form=Sign+In" & TextBox1.Text & "&password=" & TextBox2.Text & "&sub_form=Sign+In"
        Dim tempCookies As New CookieContainer
        Dim encoding As New UTF8Encoding
        Dim bytedata As Byte() = encoding.GetBytes(postdata)

        Dim postreq As HttpWebRequest = DirectCast(WebRequest.Create("https://122.52.209.250/login.do"), HttpWebRequest)
        postreq.Method = "POST"
        postreq.KeepAlive = True
        postreq.CookieContainer = tempCookies
        postreq.ContentType = "application/x-www-form-urlencoded"
        postreq.Referer = "https://122.52.209.250/login.do"
        postreq.UserAgent = "Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.16) Gecko/20110319 Firefox/3.6.16"
        postreq.ContentLength = bytedata.Length


        Dim postreqstream As Stream = postreq.GetRequestStream()
        postreqstream.Write(bytedata, 0, bytedata.Length)
        postreqstream.Close()

        Dim postresponse As HttpWebResponse


        postresponse = DirectCast(postreq.GetResponse(), HttpWebResponse)
        tempCookies.Add(postresponse.Cookies)
        logincookie = tempCookies

        Dim postreader As New StreamReader(postresponse.GetResponseStream())

        Dim page As String = postreader.ReadToEnd

        WebBrowser1.DocumentText = page

    End Sub



    Function CertificateValidationCallBack(ByVal sender As Object, _
        ByVal certificate As System.Security.Cryptography.X509Certificates.X509Certificate, _
        ByVal chain As X509Chain, _
        ByVal sslPolicyErrors As Security.SslPolicyErrors _
    ) As Boolean

        Return True
    End Function

    Private Sub MakeRequest()

        'Set the callback
        ServicePointManager.ServerCertificateValidationCallback = New RemoteCertificateValidationCallback(AddressOf CertificateValidationCallBack)

        'Make the request

    End Sub
    Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
        'WebBrowser1.DocumentText = RichTextBox1.Text



    End Sub
End Class

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hi to all kindly check my syntax in passing a security certificate if it's right or wrong thanks in advance