If rekordbox is in EXPORT mode, it cannot be controlled from the unit. Click the part indicated by [EXPORT] at the top left of rekordbox screen and then select [PERFORMANCE].

If your computer is a Mac, disconnect the USB cable, start the [Audio MIDI Setup] utility software of OS X and display the MIDI window or MIDI studio. Select the [DDJ-1000] icon and then click [Remove Device]. (The icon may be [USB MIDI Device] instead of [DDJ-1000]. If so, select [USB MIDI Device].) Connect with the unit using the USB cable again.