That's not an error we've heard of, and there are lots of users using JFBConnect on Joomla 3.x, so we'll need to know more about what may be happening on your site.
Can you tell me:
* Was this an initial installation, or were you trying to upgrade from a previous version of JFBConnect?
* Is the site an original Joomla 3.x site, or did you migrate from Joomla 2.5?
Any other information you can provide about the history of your site and JFBConnect on it may help.
Thanks,
Alex