C# Restful client - connection timeout

I'm using WinForms and accessing my Restful webservice. For some reason the code after a while breaks, by giving the timeout error while connecting to the server.

The problem might also be due to my code design. Here's my Restful client class

public class Restful
{
    public string auth = "Basic " + Convert.ToBase64String(Encoding.Default.GetBytes("MyUserName:MyPassword"));
    
    public string POST(string parameters)
    {
         var request = (HttpWebRequest)WebRequest.Create("http://myserverdomain.com/api/webservice/someMethod");

        byte[] byteArray = Encoding.UTF8.GetBytes(parameters);

        request.Method = WebRequestMethods.Http.Post;
        request.Headers["Authorization"] = this.auth;
        request.ContentLength = byteArray.Length;
        request.ContentType = "application/x-www-form-urlencoded";

        Stream postStream = null;

        try
        {
            // ERROR IS IN THIS LINE
            postStream = request.GetRequestStream();
        }
        catch (WebException ex)
        {
            // I'm kind of creating an hack here..which isn't good..
            if (ex.Status.ToString() == "ConnectFailure")
            {
                System.Threading.Thread.Sleep(1000);
                this.POST(parameters);
            }
        }

        if (postStream == null)
            return string.Empty;

        postStream.Write(byteArray, 0, byteArray.Length);
        postStream.Close();

        using (var response = (HttpWebResponse)request.GetResponse())
        {
            var responseValue = string.Empty;

            if (response.StatusCode != HttpStatusCode.OK)
                return responseValue;

            using (var responseStream = response.GetResponseStream())
                if (responseStream != null)
                    using (var reader = new StreamReader(responseStream))
                        responseValue = reader.ReadToEnd();

            return responseValue;
        }
    }
}

I'm receiving the error (after a few successfully send items):

Unable to connect to remote server

A connection attempt failed because the connected party did not properly respond after a period of time, or established connection failed because connected host has failed to respond MyServerIpAddress

Sometimes I send thousands of items to the server, sometimes I only send 2 or 4. So I call this POST function within a loop.

try
{
    foreach (app.views.Documents doc in DocumentsView)
    {
        var parameters = "key=" + doc.key;
            parameters += "&param1=" + doc.param1 + "&param2=" + doc.param2;
        
        /*
         * Validates the response of Restful service.
         * The response is always in JSON format.
         */
        if (response(Restful.POST(parameters)) == false)
        {
            MessageBox.Show("Error while sending the ID: " + doc.id.ToString());
            break;
        };
    }
}
catch (Exception ex)
{
    MessageBox.Show("Error while sending documents: " + ex.Message);
}