调试此代码片段时，会发生此错误

调试此代码片段时，发生此错误（无法连接远程服务器）。我显示了评论行中发生错误的位置

private static string GetWebText(string url)
    {
        HttpWebRequest request = (HttpWebRequest)HttpWebRequest.Create(url);
        request.UserAgent = "A .NET Web Crawler";
        WebResponse response = request.GetResponse();//errors occured here
        Stream stream = response.GetResponseStream();
        StreamReader reader = new StreamReader(stream);
        string htmlText = reader.ReadToEnd();
        return htmlText;
    }