Can't play music
"Syncronize to continue your music subscription"
is normally an indicator of the following causes, depending on the source and type of the music that you have on your M240:
(1) If your music files came from a subscription music service provider
(Napster,Yahoo, Rhapsody for example):
This would mean that the licenses for these subscription songs need to be updated. They must be updated at least once every 30 days. You must use your subscription music service's software to resync the songs (the process varies depending on the service). Also, you would get that "sync" notice if you've cancelled your subscription.
(2) If your music files were ripped from an audio CD:
The best solution would be to once again "Rip" these audio CD files using Windows Media Player, version 10 or 11. Before ripping, ensure that the "Copy Protect Music" option is unchecked by going to Windows Media Player's "Tools", then "Options", then selecting the "Rip Music" tab.
If all else fails, the best "last resort" would be by setting the M240 to MSC mode and formatting it in Windows Explorer or "Disk Management"
I hope this proves useful. I know it's quite a bummer when you have a whole bunch of songs just sitting in your player with a "Sync" error.