Ember pre-render: timed out while initializing

I am trying to create a pre-render server for my ember app.

I installed ember-prerender (http://ift.tt/1RXQQgH), used the initializers provided in the /example, deployed it on one of my servers.

But when I try to launch it:

Restarting renderer, timed out while initializing

This is the case even if I change engine (I tried with Phantom and jsdom).

My best guess is that the XContentReady event is never fired.