I can't program the drum pads on my keyboard

In order to program the drum pads on your keyboard, you will want to change the drum pads so that they are sending MIDI CC Data (preferably on a different channel than what the keyboard keys are sending on too).

You will also want to make sure the CC # you are having them send is not a common CC # for other uses (use #'s ranging from 14 to 31).

After you have done this, you will want to assign the drum pads in the MainStage Layout mode.