Umm.. That's a new error to us. Can you tell us:
* Are you trying to register using JFBConnect's "Login With Facebook" button?
* Are you trying to create a new user (using the righthand side of the Login/Register) page, or login and connect to an existing Joomla user (the left hand side)
* Do you have any security type extensions installed (Firewall, AdminTools, HackGuard, etc)?
Thanks,
Alex