There are a few causes that can cause this error:
1. Please make sure that you have turned on the Google+ API switch for your app.
2. Please turn off any SEF extensions for the JFBConnect component.
3. Also, can you enable the "Use OpenID if No Google+ Profile Exists" setting in the JFBConnect -> Configuration -> Google area?
If these suggestions don't work, in the Configuration area, set "Enable Debug Mode" to "Yes". If there are additional error messages during registration, let me know what they are so we can investigate further.
-Melissa