后台下载报错ThrowForNonSuccess HRESULT:0x80072EFD

Question

每次都会报错。

代码如下：

StorageFile destinationFile = await KnownFolders.PicturesLibrary.CreateFileAsync("1.rmvb", CreationCollisionOption.ReplaceExisting);
            BackgroundDownloader downloader = new BackgroundDownloader();
            download = downloader.CreateDownload(new Uri("ftp://ygdy8:[e-mail]:8005/[阳光电影www.ygdy8.com].里约大冒险2.BD.720p.中英双字幕.rmvb"), destinationFile);
            try
            {
                await download.StartAsync().AsTask(cts.Token, progressCallback);
            }
            catch (Exception)
            {
                Log("Download Exception.");
            }

错误信息如下：

at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification(Task task)
   at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult()
   at 后台传输任务.MainPage.<Start>d__0.MoveNext() in d:\wjm\project4.5\WIN8\后台传输任务\后台传输任务\MainPage.xaml.cs:line 66

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