did you disconnect the negative terminal of the battery before you changed the cat? if not then disconnect it and leave it disconnected for about 15/20 minutes, thsi resets the ecu, start the engine and leave it idling for a few minutes in order for the ecu to detect the changes made to the cat...i dont know why the map sensor is effected though, but if the check light comes back on then check that the map sensor(on top of the intake manifold) is secure, failing that bring it to your local dealership