title: NSNetwork error after starting NSURLSessionDownloadTask
body: <p>I use <code>NSURLSession</code> to download files in background. Here is how I start a new  <code>NSURLSessionDownloadTask</code>:</p>
  
  <pre><code>NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[self nextURL]];
  _task = [[self downloadSession] downloadTaskWithRequest:request completionHandler:nil];
  [_task resume];
  </code></pre>
  
  <p>After calling <code>resume</code>, I encountered the following error:</p>
  
  <pre><code>nsnetworkd[1557] &lt;Error&gt;: Couldn't add download &lt;SSDownload: 0x16d63a20&gt;: 958545229883046269 to download manager
  </code></pre>
  
  <p>After this, no <code>delegate</code> methods were called (it seems like the session was killed). The internet connection was ok (Safari was able to open websites).</p>
  
  <p>It occurred only once on iOS 7.0.4. Can someone please explain what could this error mean? Is this an iOS 7.0.x bug or is there a good workaround?</p>