Facebook login does not work for several users

I tried to test on your page, but when I did, the following error from Facebook appeared:

This app is in sandbox mode. Edit the app configuration at developers.facebook.com/apps to make the app publicly visible.

To fix, please go into your Facebook Developer Area and set "Sandbox Mode" to "disabled".

While in Sandbox mode, authentication will only work for admins of your app.

I hope that helps, but if not, let us know.

Thanks,
Alex