I'm going into the realm of guesswork here as this functionality I've not used yet, but I'm wondering if something of your Facebook App is misconfigured. When first clicking on Sign in with Facebook, it should give a popup with basically a handshake saying "Yes, I allow this site to talk to Facebook and do the following things with my account". I can see it trying to do that with the following permissions parameters in the popup URL:
&scope=publish_stream%2Cpublish_actions%2Cemail%2Cuser_birthday%2Cuser_relationships&display=popup
The most I can try to do is replicate the issue on my site, but while we're waiting on SI to respond (really delayed responses given it's the weekend now), double-check your API config on your site and the settings defined on your Facebook App.