DIAGNOSIS The machine is detecting an 'overheating' condition in the carafe heating plate. It's a safety shutoff. This usually happens because the plate is already hot from a recent brew cycle or there's a minor fault in the thermostat.
FIX Let the machine cool down completely—unplug it for at least 30 minutes. When you plug it back in, try brewing a carafe immediately, before the warming plate has a chance to pre-heat. Use cold water in the reservoir. If it works, the issue is just thermal overload.
IF THAT DIDN'T WORK Check that you're using the official Keurig carafe or one that's perfectly flat on the bottom. An uneven or warped carafe won't make full contact with the heating plate, causing it to heat unevenly and trip the sensor.
HEADS UP The 'Keep Warm' function for the carafe plate can contribute to this. If it happens often, turn off the 'Keep Warm' setting in the menu (press Menu, then navigate to Carafe Settings) so the plate only heats during the actual brew cycle and for 30 minutes after.