@Mark, Sorry that was poorly explained. The plugin is working fine. I have updated the facebook.php file and is still working fine. However, I did get the same email from Facebook today stating "fix within 48hours etc". I am not sure if updating the facebook.php file fixes this legacy authentication issue of if it is only a perceived issue on Facebook's behalf. Either way they sent me an email and it is their policy, so if anyone has a fix, please yell out.
Thanks for taking the time to respond.
@Mark Bridges - I am actually using http://community.elgg.org/pg/plugins/project/595745/developer/MisterBridges/facebook-connect-for-173 right now but I still rx'd the notice from Facebook. Regardless, thank you for your comment.
@Deep Shah - i've changed the Facebook.php file, thank you for sharing the link.
@Nick - Let us know what happens, i'll do the same.
As you can see, it is about 8 days since the original post. I have updated the facebook.php file as stated above and have not had my site login blocked. I don't know if this fixed the problem or if Facebook haven't gotten around to blocking it yet. Hope it is the former.