That was a bug with JFBConnect v4.3. It's been fixed in v5.0.. Basically, the update-server address we had in the 4.3 version had a space before it, which was causing problems. When you update the extension, the new update server address is not set in Joomla though (which is annoying).
However, if you uninstall JFBConnect and then re-install it, that will properly set the Joomla update server to the proper address and that message will go away. When you uninstall, that will disable the authentication, user, and system plugins.. so you'll need to re-enable them after you install again. All your settings will remain intact though.
Hope that helps,
Alex
Joomla Updater Error
Glad that got it going for you. It was a silly mistake on our part, and hopefully won't be a problem going forward.