What version of Serato DJ and MixEmergency are you using? Why don't you have Serato DJ enabled? You will want to go into the MIDI mapping mode, click on the crossfader in MixEmergency, and make sure that nothing is mapped to the crossfader (i.e. the pop-up MIDI mapping window should be red, not green). Then, make sure that Serato DJ is running (and that you're able to play/scratch video using your controller). Is the crossfader still jumping around?