I'm not sure exactly what you're trying to do... Does the overview page of JFBConnect work? Is it just the Configuration page that is throwing that error, or is it all of the admin pages?
From the looks of that error, it seems like Joomla is restricted edit access to JFBConnect. That's not something we've seen before, and we don't have logic to check for user-levels when editing. So, something seems to be restricting things, but not sure what.
Finally, as for the "I was playing with some settings", were those in JFBConnect or settings in Joomla itself? Knowing what you were doing may help us narrow things down.
Thanks,
Alex