This was an issue introduced in the latest release that we're narrowing down. It affects a few sites. If you're interested in a quick code change that should fix it for you, please try the following:
* Edit the /components/com_jfbconnect/libraries/provider/facebook.php file
* Around line 202, you'll see:
$params['access_token'] = JFBCFactory::usermap()->getUserAccessToken($uid, 'facebook');
Change that to:
$jid = JFBCFactory::usermap()->getJoomlaUserId($uid, 'facebook');
$params['access_token'] = JFBCFactory::usermap()->getUserAccessToken($jid, 'facebook');
Please let us know how that goes for you. We've done some testing and it fixes the issue, but we'd love to hear your results as more confirmation is better.
Thanks,
Alex