2001 E320 radio locked up
 

My wife was turning down the volume via the steering wheel control, and she said it went silent and a bunch of E's apeared on the display. The radio now is for a lack of a better word, frozen on that station, on, no sound, and none of the controls on it are working. Can't turn it off either.
Any ideas?

Update: R&R the fuse, entering the code, fixed the problem. Looks like it needed a reboot (maybe running Windows internally :-)