Can you let us know a lot more details about when you received that error? Does it happen when you simply load your site? Does it happen when you are trying to authenticate and login using a social network? Is the whole page blank with that message, or is it displaying in a Joomla error-box within your template?
The only think I can suggest without knowing any other details is trying to set the "Disable SSL Verification" within the JFBConnect -> Configuration area. I don't know if that will make a difference, but may help.
Thanks,
Alex