Official comment
The problem isn't the CDJ or rekordbox, but the export database has an issue. If the drive is formatted FAT32 it's possible that you removed the drive without ejecting / stopping it first and the database was in use at the time, thus damaging the file. My recommendation would be to format the drive and re-export the contents from rekordbox.
Also note that 6.6.4 is the current version, so you may consider updating.