Trying to find out if the url is valid ? Use the following code:

 public static bool urlExist(string url)
        {
            WebRequest webRequest = WebRequest.Create(url);
            WebResponse webResponse;
            webRequest.Timeout = 1500; // Max timeout
            try
            {
                webResponse = webRequest.GetResponse();
            }
            catch //If exception thrown then couldn't get response from address
            {
                return false;
            }
            return true;
        }