HttpListenerException通过Webclient从C#控制台应用程序从网站下载图像时出错

我想通过C#控制台应用程序中的webclient下载图像，但它在Httplistener中抛出错误，无法下载图像。我甚至用网络浏览器下载，但失败了。如有任何建议，将不胜感激

   try
        {
            using (WebClient fileReader = new WebClient())
            {
                fileReader.Headers.Add("User-Agent", "Mozilla/5.0 (Windows NT 5.1; rv:25.0) Gecko/20100101 Firefox/25.0");
                fileReader.Headers.Add("Accept-Language", "en-US,en;q=0.5");
                fileReader.Headers.Add("Accept-Encoding", "gzip,deflate");
                fileReader.Headers.Add("Accept", "text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8");
                strFilename = strSaveAs.ToString().Trim() + ".jpg";

                if (System.IO.File.Exists(returnImg) == false)
                {
                    fileReader.DownloadFile(strURI, returnImg);
                    Console.WriteLine("Finished downloading image " + strFilename.ToString());
                }
            }

        }
        catch (HttpListenerException ex)
        {
            Console.WriteLine("Error accessing " + strURI + " - " + ex.Message, true);
            //throw;
            returnImg = null;
        }

        catch (Exception ex)
        {
            Console.WriteLine("Error accessing " + strURI + " - " + ex.Message, true);
            //throw;
            returnImg = null;
        }

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错误是什么？为什么失败？@ChrisLava，我遇到了这个错误：在WebClient请求期间发生了异常。