Fb account no authenticated.

I'm trying to log in to prezi using my fb account where all of my prezis are stored. This is what it is telling me:
"Hey,

There was a problem authenticating you with Facebook, sorry.

You may try signing up or log in with your username and password.

If you don't remember your Prezi.com password you can create a new one.

In case you think the problem is on our side don't hesitate to request for help on our support channels."