async void worker_DoWork(object sender, DoWorkEventArgs e) { BackgroundWorker worker = new BackgroundWorker(); string ssmlText = "<speak version=\"1.0\" "; ssmlText += "xmlns=\"http://www.w3.org/2001/10/synthesis\" xml:lang=\"es-ES\">"; ssmlText += strTextoALeer; ssmlText += "<mark name=\"fin\"/></speak>"; AppResources.ss.SpeakSsmlAsync(ssmlText); await worker.RunWorkerTaskAsync(); }