Hello Todd,
I see the failed log-in attempts in the logs, but no details that could explain why this happened.
Did you follow the instructions at
http://kb.x-cart.com/display/XDD/Setting+up+Facebook+Login+for+your+store ?
It may be that your Facebook app is not configured to accept requests from your site's domain.
If this doesn't help, you need someone who could debug the problem right on your server. Our support team can do this for you:
support@x-cart.com