This should be the manual for your unit:http://www.m-audio.com/images/global/ma ... N01_V1.PDF
Here's the manual for the newer 49 and 61-key keyboards:http://www.m-audio.com/images/global/ma ... t08_EN.pdf
You have to assign CC#'s to the buttons. The procedure is described on page 10 of the old manual. Don't know why they're not already programmed. All of the buttons on my unit were CC#0 from the factory.
Here's what I would do to assign buttons on your keyboard:
1) Press 'Advanced'
2) Press 'Ctrl Assign' (your low C note)
3) Press the Control Button you wish to program
4) Press in the CC# you wish to assign to the button
--- use the white keyboard keys in your upper octaves to select numbers
--- I suggest programming each button to the same number written below it
5) Press the Enter key (your high C note)
6) Repeat for each button you want to program
Now go back into Control Surfaces in Mixcraft and 'learn' those buttons in!