I received the message 'This song could not be played'. This message is displayed for one of the following reasons - 1. The track is DRM Protected. iOS prevents app's from reading the content from DRM protected media files. If you have a lot of DRM Protected music, please enable the 'DRM Filter' option in Settings. 2. The track is of duration 0 seconds. This can sometimes occur when a track is extracted incorrectly from a scratched CD, for example. 3. The track is in the cloud and is currently downloading to the device. The final URL (address) of the track is only set once the track has completely downloaded. Once the track is fully downloaded, re-select it in the app before attempting to play it. 4. The track has become corrupt in some other, undefined way. For these tracks, it is best to delete them via the Music app, and then re-sync the device, or download the track again. 5. There is one further rare case for Cloud based tracks. If a track was in the Cloud, and began downloading to the device but didnt complete, then this track wont be playable until the download completes. In theory, playing the track in the Music app should re-initiate the download so it completes, but I generally just delete these tracks and re-download them, or sync them across fresh from iTunes.