You mentioned that it worked fine twice, but not a third time. These cruise units are very sensitive to ground. Make sure the ground wire to the actual hand control is not pinched in the clamp. I found this on 3 different bikes.
Taking up the throttle cable slack is always important whenever you take the hand control apart. This is most comon with changing of grips and such. If you added the cruise after the bike came from the factory, chances are you do need to adjust the slack in the cable and re-initialize. Remember, one of the things used by the ECM and the cruise control is TPS (Throttle position sensor)