HttpWebRequest.GetResponse: "The main connection was closed: An unexpected error occurred while receiving."

Question

HttpWebRequest.GetResponse: "The main connection was closed: An unexpected error occurred while receiving."

I wrote a Windows C # service (.NET Framework 3.5, C # 3.0) that sends files and HTML form information to a remote server, and then stores the XML server response in a database. Here is the main piece of relevant code:

    HttpWebRequest request = WebRequest.Create(postUrl) as HttpWebRequest;

    request.ProtocolVersion = HttpVersion.Version10;
    request.KeepAlive = false;
    request.Timeout = 600000;
    request.ReadWriteTimeout = 600000;
    request.Method = "POST";
    request.ContentType = contentType;
    request.UserAgent = userAgent;
    request.CookieContainer = new CookieContainer();
    request.ContentLength = formData.Length;

    using (Stream requestStream = request.GetRequestStream())
    {
        // Push it out there
        requestStream.Write(formData, 0, formData.Length);
        requestStream.Close();
    }

    return request.GetResponse() as HttpWebResponse;

My service works correctly for all small files, but when I try to send larger files (8-9 MB), the following error occurs.

    The underlying connection was closed: An unexpected error occurred on a receive.

I looked at the outgoing request using Fiddler and was able to get the following information:

    HTTP/1.1 504 Fiddler - Receive Failure
    Content-Type: text/html
    Connection: close
    Timestamp: 12:25:04.067

    ReadResponse() failed: The server did not return a response for this request.