Httpwebrequest hilfe beim Upload auf .php

[spiTe-checKer]

Hallo Leute, ich habe vor eine Datei per httprequest auf einen Webspace zu schicken. Leider funzt das irgendwie nicht - er läd manchmal einfach nur eine Leere Datei hoch.
Unter anderem gibt er mir als Response auch nur den Quelltext aus, nicht aber den download link, danke für die Hilfe!

       'File einlesen
        Dim location As String = "C:\Dokumente und Einstellungen\xxx\Desktop\testing\bla.txt"
        Dim b = txt_ReadAll(location)
        Dim Endung As String = fRight(location, (location).Length - InStrRev(location, ".") - 1)
        Dim boundary As String = CreateBoundary()

        Dim req As Net.HttpWebRequest = Net.HttpWebRequest.Create("http://www.xxx/exec/xupload.php")
        req.Credentials = System.Net.CredentialCache.DefaultCredentials
        req.Method = "POST"
        req.UserAgent = "spiTe-checKer/1.10 (Windows 7; U; de)"
        'req.Headers.Add(HttpRequestHeader.Host, 
        req.Accept = "Accept: application/xhtml+voice+xml;version=1.2, application/x-xhtml+voice+xml;version=1.2, text/html, application/xml;q=0.9, application/xhtml+xml, image/png, image/jpeg, image/gif, image/x-xbitmap, */*;q=0.1"
        req.Headers.Add(Net.HttpRequestHeader.AcceptLanguage, "de-DE,de;q=0.9,en;q=0.8")
        req.Headers.Add(Net.HttpRequestHeader.AcceptCharset, "iso-8859-1, utf-8, utf-16, *;q=0.1")
        req.Headers.Add(Net.HttpRequestHeader.AcceptEncoding, "deflate, gzip, x-gzip, identity, *;q=0")
        req.Referer = "xxx"
        req.KeepAlive = True
        req.Connection = "TE"
        req.Headers.Add(Net.HttpRequestHeader.Te, "deflate, gzip, chunked, identity, trailers")
        req.ContentLength = (b).Length + 449 'bist das File
        req.ContentType = "Content-Type: multipart/form-data; boundary=" & boundary
        req.ServicePoint.Expect100Continue = False

        Dim boundarybytes() As Byte = System.Text.Encoding.ASCII.GetBytes("--" & boundary & Environment.NewLine)

        Dim postData As New StringBuilder
        postData.AppendLine("Content-Type: multipart/form-data; boundary=" & boundary)
        postData.AppendLine("")
        postData.AppendLine("--" & boundary)
        postData.AppendLine("Content-Disposition: form-data; name=""F1""; filename=""bla.txt""")
        postData.AppendLine("Content-Type: " & MIMEFileType(Endung))
        postData.AppendLine("")
        postData.AppendLine(b)
        postData.AppendLine("--" & boundary)
        postData.AppendLine("Content-Disposition: form-data; name=""MAX_FILE_SIZE""")
        postData.AppendLine("")
        postData.AppendLine("5000000")
        postData.AppendLine("--" & boundary)
        postData.AppendLine("Content-Disposition: form-data; name=""passwort""")
        postData.AppendLine("")
        postData.AppendLine("testing")
        postData.AppendLine("--" & boundary)
        postData.AppendLine("Content-Disposition: form-data; name=""tn_size""")
        postData.Append("--" & boundary & "--")
        Dim infobytes As Byte() = Encoding.ASCII.GetBytes(postData.ToString)

        req.ContentLength = boundarybytes.Length + infobytes.Length

        Dim fileinfo As New IO.FileInfo(location)
        req.ContentLength += fileinfo.Length

        Dim reqstream As IO.Stream = req.GetRequestStream
        'Request ausgeben lassen zur Kontrolle'
        MsgBox(req.Headers.ToString)
        reqstream.Write(boundarybytes, 0, boundarybytes.Length)
        reqstream.Write(infobytes, 0, infobytes.Length)

        Dim FileStream As IO.FileStream = IO.File.Open(location, _
        IO.FileMode.Open)

        Dim buffer(1023) As Byte
        Dim bytesRead As Integer

        Do
            bytesRead = FileStream.Read(buffer, 0, buffer.Length)
            reqstream.Write(buffer, 0, bytesRead)
        Loop Until bytesRead = 0

        FileStream.Close()
        reqstream.Close()


        Dim resp As Net.HttpWebResponse = req.GetResponse
        Dim reader As IO.StreamReader = New IO.StreamReader( _
        resp.GetResponseStream())


        Dim responseFromServer As String = reader.ReadToEnd()
        'Kontroll MSG-Box'
        Debug.WriteLine(responseFromServer)

        'Zur Kontrolle noch einmal in eine txt Datei'
        'Dim oSW As New IO.StreamWriter(location)

        'oSW.Write(responseFromServer)
        'oSW.Close()

        reader.Close()
        resp.Close()