Again, I'm unsure what's happening here. The Canvas area is setup correctly in your Facebook App and everything seems to be working as it should. If I disable the JFBCSystem plugin, the page still remains blank within Facebook. Our system plugin is what enables all JFBConnect functionality. So, if it still is a problem with our plugin enabled, it means something outside of JFBConnect that's preventing the page from loading.
Do you still have mod_security enabled in some form on your site or some other server level firewall that could be preventing the page from loading? I've taken a picture of what's loading in Facebook below and you can see that your URL is in the form, as it should be, but the head and body sections are completely blank. So, something is preventing your server from returning any data:
I've disable Akeeba and enabled Error Reporting with the Joomla Global Configuration area and nothing is helping to indicate what is going wrong. Again, it seems like something on the server is preventing a connection to your site, but I'm not sure what.
I hope that helps explain things a little, but again, let us know if there's any more we can help with.
Thanks,
Alex