Can you go to the JFBConnect -> Configuration -> Facebook area and make sure the "Show 'Login Credentials' in Popup" setting is 'Yes'. If that is no, then the user will be redirected to Facebook to authenticate (or even verify they have already logged in) and it can break the custom Open Graph Action buttons.
Beyond that, make sure you're testing with the Facebook Admin for your app so that you can use your un-approved object and actions. Otherwise, Facebook will have issues if general (non-admin) users are trying to trigger actions.
Hopefully that helps get you going, but should you still have issues, just let us know.
Thanks,
Alex