DIAGNOSIS The machine thinks you haven't completed the cleaning cycle, or the internal timer for the reminder hasn't been reset.
FIX The official reset sequence is specific. With the machine ON, press and hold the "Sonic Ice" button and the "Light" button simultaneously for about 5 seconds. You'll see the lights on the front flash. Release the buttons. The clean indicator light should turn off.
IF THAT DIDN'T WORK Sometimes you need to do a full power cycle. Unplug the machine from the wall, not just turn it off. Wait 60 seconds, then plug it back in. Turn it on. If the clean light is still on, try the button combo again immediately after the reboot.
HEADS UP Don't just ignore it. If the clean light is on, the machine will eventually stop making ice and just flash lights at you as a reminder. It's a hard-coded lock-out.