download xls file over https vb.net

I'm trying to download an xls file from an https website, even though I am passing the username and password to the site, when I download the file I am gettting the "You have reached a secure web page, please login" page instead of the xls file.  What do I need to do to properly login to the site and get past the SSL security?  Here is my code:

        Dim dt1 As Date = DateAndTime.Now
        Dim Req As HttpWebRequest
        Dim SourceStream As System.IO.Stream
        Dim Response As HttpWebResponse
       Dim URL As String = "https://www.xxxxxxxx.com/Conduit/UI/SSL/RatesPricing/xxxxxxx.aspx? FileType=xls"
        Req = HttpWebRequest.Create(URL)
        Req.Credentials = New NetworkCredential("username", "password")
       Response = Req.GetResponse()

       SourceStream = Response.GetResponseStream()
        Dim inBuf(100000) As Byte
        Dim bytesToRead As Integer = CInt(inBuf.Length)
        Dim bytesRead As Integer = 0
        While bytesToRead > 0
            Dim n As Integer = SourceStream.Read(inBuf, bytesRead, bytesToRead)
            If n = 0 Then
                Exit While
            End If
            bytesRead += n
            bytesToRead -= n
        End While

        Dim fstr As New FileStream("C:\Rates\xxx.xls", FileMode.OpenOrCreate, FileAccess.Write)
        fstr.Write(inBuf, 0, bytesRead)
        'str.Close()
        SourceStream.Close()
        fstr.Close()Start Free Trial