Error: "you must write contentlength bytes to the request stream before calling begin getresponse" on webrequest

Hi,

I have this webrequest looking like this:

 Public Sub SendFile(ByVal filename As String)
            coRequest = CType(WebRequest.Create(sURL), HttpWebRequest)
            coRequest.ProtocolVersion = TransferHttpVersion
            coRequest.Method = "POST"
            coRequest.ContentType = "multipart/form-data; boundary=" & BeginBoundary
            coRequest.Headers.Add("Cache-Control", "no-cache")
            coRequest.KeepAlive = True
            Dim strFields As String = GetFormfields()
            Dim strFileHdr As String = GetFileheader(filename)
            Dim strFileTlr As String = GetFiletrailer()
            Dim info As FileInfo = New FileInfo(filename)
            coRequest.ContentLength = strFields.Length + strFileHdr.Length + strFileTlr.Length + info.Length
            Dim io As System.IO.Stream
            io = GetStream()
            WriteString(io, strFields)
            WriteString(io, strFileHdr)
            Me.WriteFile(io, filename)
            WriteString(io, strFileTlr)
            GetResponse()
            io.Close()
            coRequest = Nothing
        End Sub

The GetResponse sub looks like this:

Public Overridable Sub GetResponse()
            If coFileStream Is Nothing Then
                Dim stream As Stream
                Dim response As WebResponse

                Try
                    response = coRequest.GetResponse()
                Catch web As WebException
                    response = web.Response
                End Try

                If response IsNot Nothing Then
                    stream = response.GetResponseStream()
                    Dim sr As StreamReader = New StreamReader(stream)
                    Dim str As String
                    ResponseText.Length = 0

                    For Each str In sr.ReadLine
                        ResponseText.Append(str)
                    Next

                    response.Close()
                Else
                    Throw New Exception("MultipartForm: Error retrieving server response")
                End If
            End If
        End Sub

The coRequest.ContentLength is 100507 and everything seems ok, but I get this error:

you must write contentlength bytes to the request stream before calling begin getresponse

I do the exact same in C#:

 public void SendFile(string filename)
        {
            // The live of this object is only good during
            // this function. Used mainly to avoid passing
            // around parameters to other functions.
            coRequest = (HttpWebRequest)WebRequest.Create(URL);
            // Set use HTTP 1.0 or 1.1.
            coRequest.ProtocolVersion = TransferHttpVersion;
            coRequest.Method = "POST";
            coRequest.ContentType = "multipart/form-data; boundary=" + BeginBoundary;
            coRequest.Headers.Add("Cache-Control", "no-cache");
            coRequest.KeepAlive = true;
            string strFields = GetFormfields();
            string strFileHdr = GetFileheader(filename);
            string strFileTlr = GetFiletrailer();
            FileInfo info = new FileInfo(filename);
            coRequest.ContentLength = strFields.Length +
              strFileHdr.Length +
              strFileTlr.Length +
              info.Length;
            System.IO.Stream io;
            io = GetStream();
            WriteString(io, strFields);
            WriteString(io, strFileHdr);
            this.WriteFile(io, filename);
            WriteString(io, strFileTlr);
            GetResponse();
            io.Close();
            // End the life time of this request object.
            coRequest = null;
        }

 public virtual void GetResponse()
        {
            if (null == coFileStream)
            {
                Stream stream;
                WebResponse response;
                try
                {
                    response = coRequest.GetResponse();
                }
                catch (WebException web)
                {
                    response = web.Response;
                }
                if (null != response)
                {
                    stream = response.GetResponseStream();
                    StreamReader sr = new StreamReader(stream);
                    string str;
                    ResponseText.Length = 0;
                    while ((str = sr.ReadLine()) != null)
                        ResponseText.Append(str);
                    response.Close();
                }
                else
                    throw new Exception("MultipartForm: Error retrieving server response");
            }
        }

And it works fine!

Does anyone have an idea why I get this error in VB.net and how I can fix it?

Thanks for your help!

Peter