It's likely that you have the System - Cache plugin enabled and it's ordered before the JFBCSystem plugin. The JFBConnect Error Checker should detect that, so I'd run that tool again. After you re-order the System - Cache plugin to be after the JFBCSystem plugin, you'll need to clear your cache and it should be fixed.
I'd still highly recommend looking into why the HTML structure of your page is so bad. There should never be multiple html, body, or head tags. If you run into other issues, that's almost surely why.
Thanks,
Alex