I just tried to register on your site and could recreate the issue.
From what I can see, you're running Joomla 3.3 and an older version of JomSocial. In that case, you're being affected by
this bug in JomSocial
. You'll need to upgrade JomSocial to fix this problem. It's not related to JFBConnect.
If you upgrade and still have the problem, just let us know, and we'll gladly help however we can.
Thanks,
Alex