You're likely running Joomla 3.0.x. JFBConnect will not work with that release. You should upgrade to at least Joomla 3.1, but preferably Joomla 3.2.1. That's the latest release of Joomla and fixes numerous bugs and, more importantly, security issues. Joomla 3.0 has not been developed or supported by Joomla.org in over a year, and is not recommended to be used at all.
I hope that helps, but if not, let me know.
Thanks,
Alex