If the Swim audio player accepts AAC audio files from the iTunes Store, is there anything unusual about the ones that it won't accept?
I can think of a few possibilities:
- Perhaps the Swim player has a limit on the maximum length of a song, and you are trying to transfer a song of unusual length.
- Perhaps you accidentally tried to transfer an offline listening copy of an Apple Music subscription song, rather than a purchased iTunes Store song. Apple Music streaming subscription files have DRM.
- Perhaps you have a really ancient 128 Kbps AAC file from the very early days of the iTunes Store. Those, too, have DRM.