Reply to APC40 not midi mapping

Hey i been trying to map my apc40 and i know typically all you have to do is going into midi mode and move a knob and get out of midi mode. For some reason this is not working? At the moment I only have my apc40 hooked straight up to ableton.
Do I maybe have my preferences wrong?
I been using the Will Marshall mapping and wanna make my own, could I been in the wrong setting?