I've seen the empeg "lock" several times now like others have reported. Every time the music keeps going, and the screen keeps updating, but it won't accept input. It has never accepted input from the front panal, or the remote for me when it does this. The last time it happened, I still had my serial console up, and it also did not respond to a "q" on the serial port, but kept spitting out the timecode. Actually looking back on the logs, it didn't even echo back anything I typed. And everytime it has happened, the hard drive indicator is on, but not showing drive activity beyond when it needs to rebuffer.

Hope this helps to track it down.