Connecting DJM 2000 to imac

Hi guys, I am having trouble connecting my DJM 2000 to my iMac which is causing me problems from using the link through rekordbox? (Dragging on dropping tunes onto cdj 2000's via rekordbox). I have had this working before but I disconnected the setup and when I have reconnected its doesn't seen to work? 

Please could you help? If you need any other info please ask! 

Regards Will