At the IPAC, swap the wires for P3 buttons 1-4 with buttons 5, 6, 8, & 9. If buttons 1-4 don't work after that, and buttons 5, 6, 8, & 9 do, then it sounds like it might be a problem with the IPAC. If the problem doesn't follow with the change, you have a wiring problem.
Are you sure this is an IPAC2 and not an IPAC4? That's a whole lot of buttons for an IPAC2...