Error: DRM protected file

You selected a music file protected by Digital Rights Management (DRM) protection for syncing. doubleTwist Sync assumes that you won't be able to play this file on your device and thus skipped transfering it.

Prior to 2009, songs that were purchased from the iTunes Store were protected by Digital Rights Management (DRM), which limits playback to "authorized" devices such as Apple iPods and iPhones. The iTunes Store has since converted to a DRM-free model and you can upgrade previously purchased songs to be non-DRM using a subscription to iTunes Match ($24.99/year). These upgraded songs can then be played on anything which supports the M4A format like Android devices.

Here's Apple's page on iTunes Match.

http://www.apple.com/itunes/itunes-match/