Check the below post for Windows and Mac mp3 repair tools. They worked for me when my Traktor crashed during a gig. I then ran my whole collection through then and they found a few problem files.
Make a copy of the faulty tracks before you fix them. Then once you have identified the problems in the tracks upload the copy from. BEFORE you fixed the track to Denon DJ, so they can look at the track data and find out why they failed and implement a bug fix so it doesn’t kill a track on a festival stage or a wedding first dance.