title: Downloading and saving a file fails after publishing app
body: <p>When I finish developing app on Windows Phone 8 in Visual Studio 2013 and start testing it on my physical device - everything works perfect. 
  After publishing app in Windows Mobile Store, when i download app on device, it giving me error in moment i want to download and save file into IsolatedStorage. This occurs in this fragment. </p>
  
  <p>I missing some permissions? Why when I debug app via VS everything is okay, but after publishing - fails?</p>
  
  <pre><code>private Task&lt;Stream&gt; DownloadFile(Uri url)
      {
          var task = new TaskCompletionSource&lt;Stream&gt;();
          var webClient = new WebClient(); 
          webClient.OpenReadCompleted += (s, e) =&gt;
          {
              if (e.Error != null) task.TrySetException(e.Error);
              else if (e.Cancelled) task.TrySetCanceled();
              else task.TrySetResult(e.Result);
          };
          webClient.OpenReadAsync(url);
          return task.Task;
      }
  
      private async Task&lt;Problem&gt; DownloadFileFromWeb(Uri uriToDownload, string fileName, CancellationToken cToken)
      {
          try
          {
              using (Stream stream = await DownloadFile(uriToDownload))
              using (IsolatedStorageFile storage = IsolatedStorageFile.GetUserStoreForApplication())
              {
                  if (storage.FileExists(fileName)) return Problem.Other;
                  using (IsolatedStorageFileStream file = storage.CreateFile(fileName))
                  {
                      const int BUFFER_SIZE = 8192;
                      byte[] buf = new byte[BUFFER_SIZE];
  
                      int bytesread = 0;
                      while ((bytesread = await stream.ReadAsync(buf, 0, BUFFER_SIZE)) &gt; 0)
                      {
                          cToken.ThrowIfCancellationRequested();
                          file.Write(buf, 0, bytesread);
                      }
                  }
              }
              return Problem.Ok;
          }
          catch (Exception exc)
          {
              if (exc is OperationCanceledException)
                  return Problem.Cancelled;
              else return Problem.Other;
          }
      }
  </code></pre>