As you probably know, Facebook for Windows Phone is actually not made by Facebook itself, but by Microsoft. That's not necessarily a bad thing, but can lead to problems such as this one, because the issue has obviously been caused by a recent change in Facebook's API. Anyways, everything should be fixed now with this new update, which should be waiting you in the Store.
Since it was Facebook that had to change something in its API, Microsoft's Corporate VP, Joe Belfiore, took to... Twitter, to express his gratitude.
Thanks to our friends at Facebook: a new FB app update is now in Store. It addresses a crash some people were hitting in the last update.— joebelfiore (@joebelfiore) April 18, 2013
You can get the latest version of Facebook for Windows Phone here!
source: Joe Belfiore via FierceMobile