Had control of Intensity on Mac 500s all day and yesterday and while trying to store cues lost control of Intensity. I can control everything else (Pan, Tilt, Gobos, etc), but can not close the shutters.
Have you tried doing both a hard reset and soft reset of the fixtures? Using the fixture's menu, can you dim them manually? With only intensity in the programmer, <pig><park> to see if you might have accidentally parked them. Is the Grandmaster /CueList fader /DBObutton up?