We've had occasional reports from users that lose connection with MP3tunes on Squeezebox devices. In our internal QA, we've sometimes encountered connection errors with a 401.. number error, but some users have reported seeing this: "Data request error: DB Error: connect failed"

See forum thread: http://forums.slimdevices.com/showthread.php?t=72763
(Reports note the Boom and Duet)

The workaround that seems to handle it for most people is to completely delete the MP3tunes app from MySqueezebox.com, and then add it again.

An alternate scenario for me has been with having two MP3tunes accounts. Generally, switching between accounts fails like above when I've tried (Saving Changes after switching on the Player Settings tab of My Apps) and the remedy has been to delete and readd the app.