Few days ago, i came across a website zoomin.com, they were giving away a 20 page free photo book for every new signup.
Without a delay, i clicked on signup button, and guess what.. i see the following error page
Obviously, soon enough i realized that the error was coming because i was not allowed to access facebook from my office. And as the site was blocked, i wasn’t even able to sign up for this website.
Then when i went home, the registration page appeared without any error, and the actual page was..
And i was able to signup successfully.
But this might not be the case with every user who lands on your signup page, they might not have access to internet where facebooking is allowed, or they may not even care to come back to your signup page again.
So just to avoid, losing potential sign up on your website, always keep a back up and allow user to chose whether they want to sign up using facebook, or directly from your website form.