So this has happened a couple of times now phones working fine then I have a look at the screen which is white-washed and it says App Error 523 with the only option being clicking reset.
After clicking reset the phone basically does a soft reset. After the phone soft resets on occasion some of my menu items have dissapeared and dont return until I do another soft reset but other times the phone just restarts and everything is fine until the next time the message comes up.
It can't be surely no new software been installed since I got it etc, I don't want to start playing about with reloading software, knowing my luck something will go wrong.
I would go to your carriers website and download the software on your computer. Also make sure that you have DM 4.6. If you reload the software I am pretty sure that the app error will go away.