title: "ValueError: Invalid async_mode specified" when bundling a Flask app using cx_Freeze
body: <p>I am building an API that uses Waitress, Flask, and Flask_SocketIO in Windows. Everything works fine from the command line, but when I try to bundle my API into an .exe using cx_Freeze and then run it, I get the error:</p>
  
  <pre><code>ValueError: Invalid async_mode specified
  </code></pre>
  
  <p>The only thing I've been able to find about this issue is a <a href="https://github.com/miguelgrinberg/python-socketio/issues/35" rel="noreferrer">python-socketio github thread</a>. There are a ton of good suggestions in that thread to try in order to fix this issue, but I've tried each and every thing but still have the same result.</p>
  
  <p>I suspect I have a missing module, but I have no idea how to find out specifically which module is missing. Does anyone have any suggestions of things to try? Even if it doesn't directly fix my problem, knowing how to drill into the stack trace to find the missing module would be helpful.</p>