Usually, that error message appears when:
* Your Facebook App isn't configured correctly. Please re-run Autotune hit "Refresh" in the FB App settings and that all settings are indicated to be correct. Mainly, your Site URL should be your home page.
* There are other Facebook integration extensions on your site that are causing conflicts. Try disabling any other widgets you might have enabled to narrow things down.
If none of that helps, please post (or Private Message) a link to a page with the login button so we can look and diagnose things.
Thanks,
Alex