get out of the habit of using comma join syntax. stick specifically with INNER and OUTER joins. The problem you encounter is mysql 5 being more conforming with sql standards.
the comma takes precedence over the LEFT (OUTER) join and thus it can't find the column inventory.album_id because it is only looking at music_albums and users and trying to perform that join first.
DATE_FORMAT(release_date,'%M %d, %Y') AS rel
LEFT JOIN inventory