Your dance floor is too close move it away from the DJ booth some sims just want to listen and watch so you got to leave room for those that want to watch ant listen. If the dance floor is too close, the ones that want to watch and listen will gather around the sides and front of the DJ booth itself and some behind. Also the NPC DJ from in the public lots in order for you to take over you got to talk to him to get him out of your way in order to DJ and than he stands right next to your sim making it impossible for your sim to move, edit when done.