Mine was doing the same thing and here is what i have found fixed it....
I have an Android tablet as well, and both the tablet and my phone have the Facebook App on them. Now i noticed when i received a notification on both the phone would get that stop message and the tablet was fine. So i experimented and had someone send me a message on Facebook, and again both devices got the notification but when i tapped on it on the phone i got the UI Stopped Working message, the tablet was fine and went right to the Facebook App.
Facebook did update on both this morning, i remember that because i went to check on a post from a friend and the phone still had the update notification showing, i cleared it without much thought as it has been updating a lot lately.
So i went through the phone starting various apps, no problem until i opened the Facebook App and promptly got the Lock Screen has stopped working message. So i uninstalled the Facebook App, and rebooted the phone just as an extra precaution, i tried plenty of reboots and such earlier and no help.
Now that the Facebook App is gone, the problem is gone... So far.... Will keep watching for problems but it appears its due to Facebook trying to send a notification that causes the crash. If your having this problem its worth a try removing Facebook.