Error message: Unable to play music title.m4a - the file //iMac/Music/Users/myname/Desktop/My iTunes Backup/iTunes/iTunes Media/Music/Artist Name/Album name/Song Title.m4a cannot be found. I can play the music on my computer, but not through Sonos. This happened after I got a new computer. The majority of my music library transferred over fine - this problem only applies to about 50 songs all in the same playlist.