That's not good. We're currently working on some decent changes to the CB plugin for these types of reasons to handle activation better when required. Until then, we should hopefully be able to get you around the issue. I'm assuming, from the above, that you have Skip CB Activation enabled, but if not, let me know.
The main time that activation might not be properly skipped is if some fields are marked as required in CB that aren't being properly filled in from Facebook. If this is an intermittent issue, I'd guess that something like "Activities" that you're trying to import from Facebook is marked as a required field in CB. If the user doesn't have this field filled out in Facebook, they return a blank field. We import this blank field, and CB is unhappy since a required field is missing. For a similar description, also see:
www.sourcecoast.com/extensions/jfbconnec...s#CB-required-fields
So, to start, please try to disable any required fields (including Avatar) from CB. With the 3.2 release, we're working on a way to automatically add required fields to the Login/Register page (if you're using Full Joomla Users).
Alternatively, since you say the "Reject writing to wall" permission seems to be at fault, if you have "Profile Permissions" as optional as well, when they reject writing to the wall, they would also be rejecting the profile permissions. In this case, it would be the same as if the profile field was blank.
Hope some of this gets you started, but if we're chasing down the wrong issue, just let us know and we can start again. Sorry for the troubles!