Were you on 3.0.2 before 3.0.3 without any issues? The change in 3.0.3 is extremely minor, and doesn't affect anything with registration or logging in, only with avatar importing after you do this.
If the page isn't loading at all, that's a different issue than the above, which was caused by the Joomla authentication plugin not being enabled. On the admin side, we intentionally don't include the Facebook javascript libraries or anything like that, so there really shouldn't be any relation between your Facebook login status vs your admin area.
Keep us posted if you have any more information or causes, and we'll poke around on our end to see if we can recreate the issue.
Thanks