Music files in AAC format cannot be played. They cannot be loaded to a crate and/or a deck. [Serato]

QuickTime of Apple is needed to play the music files in AAC format.

Please install QuickTime into your computer.

After installing QuickTime, launch Serato DJ and untick "Show iTunes Library" in Library + Display on SETUP window on Serato DJ.

Then, tick it again to start using these files.

Please update iTunes to the latest version.

Also, please see the FAQ in the Serato website from the link:

iTunes and QuickTime are trademarks of Apple Inc., registered in the U.S. and other countries.