Facebook OAuth Dialog not redirecting to login

I'm using the Facebook OAuth Dialog (reference here) to initiate a login to Facebook for my app when they click on a button.

Normally, this works. However, just a few hours ago, I realised that instead of sending me to a popup to login, the URL sends me to this page:

Any clues as to whether my code is doing something wrong? Or could there be something wrong with Facebook's redirect?

It has started working now. I am surprised to see how facebook took a such a long time to fix this. Millions of websites use facebook connect.