Login for Facebook - empty response

[Jozsef]

Hi there, I'm having trouble with @ryan's Login for Facebook module. I setup both the app and the module and it seem to work to a point.
When I click on the Login with Facebook button, it takes me to Facebook, the app presents the authentication and upon approval, it takes me back to the site.

Instead of logging me in, it doesn't create any user instead responds with an error message: "Returned facebook user data has no user ID".
Upon inspection of the module code (no great PHP skills here) it looks like there's a valid response but the user data is empty.

Does anyone have similar trouble? Where do you suggest me to look? How to debug it?

This is the page: http://debsireland.com/ticketing/login-facebook
The Facebook app settings are attached.