The line you're mentioning is where JFBConnect is trying to initialize a Community Builder field. We initialize the fields that are marked as registered, published, and set for show in profile within Community Builder to get them ready to display on the registration flow for JFBConnect.
Can you check the fields in CB that match those settings (registration, published, profile) and see if there are any non-standard fields that are set that way? The error seems to indicate that JFBConnect isn't able to initialize the field. We test with almost all types of CB fields, so I'm ont sure why that would be happening, but if you installed a special plugin for fields or something like that, it may be the cause of the problem.
When I view your normal CB Registration page, the field that stands out is "Invite Code". Can you try unpublishing that field (temporarily) and see if that at least fixes the problem? If so, let me know what type of field that is in CB and we can investigate further.
Thanks,
Alex