Hwo do I resolve a "A connection attempted failed..." exception when using HttpWebRequest?

I've created a site that acts as a proxy for mobile devices for a client's existing site. Everything seems to be working fine but when I deploy the application to the server, after a seemingly random amount of time I am no longer able to log in. I should mention that by "logging in," I am passing my login information to the client's login form and parsing the result to evaluate a successful log in.

I am using a series of HttpWebRequest and HttpWebResponse objects accomplish this. While running my application locally, I never have a problem with this. However when deployed, after a while the application will throw a WebException often with the following inner exception:

"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 (IP address appears here)"

I'm attaching a sample of the code I'm using to accomplish this as well as some details which may or may not be important:

* I am using a cookieless session state.
* I am using HTTPS to communicate with the client but I have tried switching to HTTP and the error still occurs.
* When the error occurs in my application, the client's site is experiencing no errors or delays.
* The server is deployed behind a load balancer.
* The client has informed me that they see nothing out of the ordinary regarding the requests coming from my application.
* Restarting IIS or republishing the application clears the error up immediately. It will eventually begin to occur again though.

I'm wondering if there is an issue with these HttpWebRequests being left open in some way and that perhaps over time they are holding open too many resources. As I stated above, a simple restart of IIS or republishing the application seems to cure this problem temporarily. I have made an extra effort to make sure that I am cleaning up my resources as best I can.

I would appreciate any possible help with this problem. I'm under a very tight time line and this error has sprung up very unexpectedly. Thank you.

PS: Also, in case this comes up, I added the following to the Web.Config file based on another suggestion:

<system.net>
  <defaultProxy>
    <proxy usesystemdefault="False" />
  </defaultProxy>
</system.net>

It has had no effect.

// *** The following is a sample of the call I'm making to the method below that throws the exception.
 
string loginVars = "email=" + Server.UrlEncode(txtEmail.Text.Trim()) + "&password=" + Server.UrlEncode(txtPassword.Text);
 
CookieContainer cc = new CookieContainer();
 
// This call throws the exception.
PageResponse resp = GetPageResponse("http://www.clientsite.com/Login", loginVars, RequestType.POST, cc, false, "MSIE 7.0");
 
// *** End Sample.
 
protected PageResponse GetPageResponse(string url, string pageVariables, RequestType requestType, CookieContainer cookieContainer,
            bool allowAutoRedirect, string userAgent)
        {
            PageResponse response = new PageResponse();
            HttpWebRequest req = null;
            Stream s = null;
 
            if (cookieContainer == null)
                cookieContainer = new CookieContainer();
 
            if (requestType == RequestType.GET)
            {
                if (pageVariables != null && pageVariables.Length > 0)
                    pageVariables = "?" + pageVariables;
                else
                    pageVariables = "";
 
                req = (HttpWebRequest)WebRequest.Create(url + pageVariables);
                req.CookieContainer = cookieContainer;
                req.Method = "GET";
            }
            else
            {
                req = (HttpWebRequest)WebRequest.Create(url);
                req.CookieContainer = cookieContainer;
                req.Method = "POST";
            }
 
            
 
            req.AllowAutoRedirect = allowAutoRedirect;
            req.KeepAlive = false;
            req.UserAgent = userAgent;
 
            if (requestType == RequestType.POST)
            {
                ASCIIEncoding enc = new ASCIIEncoding();
                byte[] outData = enc.GetBytes(pageVariables);
                req.ContentType = "application/x-www-form-urlencoded";
                req.ContentLength = outData.Length;
 
                s = req.GetRequestStream();
                s.Write(outData, 0, outData.Length);
 
                if (s != null)
                {
                    try { s.Close(); }
                    catch (Exception) { }
                    s = null;
                }
            }
 
            HttpWebResponse resp = (HttpWebResponse)req.GetResponse();
 
            using (StreamReader sr = new StreamReader(resp.GetResponseStream()))
            {
                response.Content = sr.ReadToEnd();
            }
 
            response.ResponseURI = resp.ResponseUri.ToString();
            response.StatusCode = resp.StatusCode;
            response.Cookies = resp.Cookies;
 
            if (resp.Headers["Location"] != null)
                response.RoutingLocation = resp.Headers["Location"];
            else
                response.RoutingLocation = "";
 
            if (resp != null)
            {
                try
                {
                    resp.Close();
                }
                catch (Exception) { }
 
                resp = null;
            }
 
            req = null;
            
            return response;
 
        }
 
        protected class PageResponse
        {
            public string Content { get; set; }
            public HttpStatusCode StatusCode { get; set; }
            public string ResponseURI { get; set; }
            public string RoutingLocation { get; set; }
            public CookieCollection Cookies { get; set; }
        }
 
        protected enum RequestType
        {
            GET = 0,
            POST = 1
        };

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