Tesla doesn't support AAC files and can't use MP3 files with "APE" tags. Some FLAC conversions also don't work. People who tend to update their software and rip themselves with the latest and greatest settings tend to run into this more often than others. I'd keep it at standard 192kbps mp3 with no ape tags and they should all work. when you start mixing and matching things like ogg, m4a, aac, mp4, etc then of course some will have issues. Mine are only flac and mp3. I've had a few flac that didn't work and I just converted them to mp3 with no issues.