SSL Error

[Dmyze]

I keep getting the following error message when trying to make an SSL Connection via VB.NET's WebRequest:

The underlying connection was closed: Could not establish trust relationship with remote server.

Private Function SendXML(ByVal xml As String) As String
 
        Dim aURL As String
 
        aURL = "https://www.site.com:10027"
 
        Dim wr As HttpWebRequest = Net.WebRequest.Create(aURL)
 
        Dim cert As System.Security.Cryptography.X509Certificates.X509Certificate
        cert = System.Security.Cryptography.X509Certificates.X509Certificate.CreateFromSignedFile("C:\cert\ca.cer")
        wr.ClientCertificates.Add(cert)
 
        wr.ContentType = "text/xml"
        wr.KeepAlive = False
 
        wr.Method = "POST"
 
        Dim sw As StreamWriter
 
        Try
            sw = New StreamWriter(wr.GetRequestStream())
            sw.Flush()
            sw.AutoFlush = True
        Catch ex As Exception
            Return False
        End Try
 
        Try
            sw.Write(xml)
            sw.Flush()
            sw.Close()
 
        Catch ex As Exception
            Return False
        End Try
 
        wr.Timeout = 900000
        Dim wres As HttpWebResponse = wr.GetResponse
 
        Dim s As IO.Stream
        s = wres.GetResponseStream
 
        Dim sr As IO.StreamReader
        sr = New IO.StreamReader(s)
 
        Return sr.ReadToEnd
 
    End Function