Web posting error "The request was aborted: The request was canceled."

req = System.Net.WebRequest.Create(uri);
        req.Credentials = System.Net.CredentialCache.DefaultCredentials;
        req.Proxy.Credentials = CredentialCache.DefaultCredentials;

        req.Method = "POST";
        req.Timeout = 2139999999;
        req.ContentType = "text/xml";       
        string text = XMLString;//Xml string
        req.ContentLength = text.Length + 1000;
        System.IO.StreamWriter writer = new System.IO.StreamWriter(req.GetRequestStream());
        writer.WriteLine(text);
        writer.Close();
        rsp = req.GetResponse();
        System.IO.StreamReader reader = new System.IO.StreamReader(rsp.GetResponseStream());
        string rp = reader.ReadToEnd();
        reader.Close();

System.Net.WebException was caught
  Message=The request was aborted: The request was canceled.
  Source=System
  StackTrace:
       at System.Net.ConnectStream.CloseInternal(Boolean internalCall, Boolean aborting)
       at System.Net.ConnectStream.System.Net.ICloseEx.CloseEx(CloseExState closeState)
       at System.Net.ConnectStream.Dispose(Boolean disposing)
       at System.IO.Stream.Close()
       at Ping.FormPostType(String uri, String buyerid) in c:\Inetpub\wwwroot\TestIceBlue\Ping.aspx.cs:line 545
       at Ping.FirstTask(String i, String uri, String buyerid, String PostT, String ResponseT) in c:\Inetpub\wwwroot\TestIceBlue\Ping.aspx.cs:line 325
  InnerException: System.IO.IOException
       Message=Cannot close stream until all bytes are written.
       Source=System
       StackTrace:
            at System.Net.ConnectStream.CloseInternal(Boolean internalCall, Boolean aborting)

HttpWebRequest Request = (HttpWebRequest)WebRequest.Create(uri); Request.Credentials = System.Net.CredentialCache.DefaultCredentials; Request.Proxy.Credentials = CredentialCache.DefaultCredentials; Request.Timeout = 2139999999; 
Request.Method = "POST"; 
Request.ContentType = "application/x-www-form-urlencoded"; 
ASCIIEncoding AscTest = new ASCIIEncoding(); 
Byte[] PostData = AscTest.GetBytes(sQryString); 
Request.ContentLength = PostData.Length + 1000; 
Request.KeepAlive = false; 
System.IO.Stream RequestStream = Request.GetRequestStream(); RequestStream.Write(PostData, 0, PostData.Length); 
RequestStream.Close(); 
System.IO.StreamReader Reader = new StreamReader(Request.GetResponse().GetResponseStream()); 
String ResultHTML = Reader.ReadToEnd();