DIAGNOSIS The machine has triggered its automatic cleaning reminder, which locks out all other functions until you run the cleaning cycle. It's a hard-coded maintenance nag, not a suggestion.
FIX You have to run the cleaning cycle. Make sure the water tank is full and the drip tray is empty and seated correctly. Press and hold the 1-Cup button for about 3 seconds until it starts blinking. The machine will start pumping water through the portafilter (you need to have the blank rubber cleaning disc inserted in the portafilter basket). Let it run its full automated cycle—it'll beep when it's done and the icon will turn off.
IF THAT DIDN'T WORK If the machine still won't exit the mode after a successful cycle, try a power cycle: turn it off at the main rocker switch on the side, wait 30 seconds, and turn it back on. If the icon is still blinking, the drip tray sensor might be dirty or obstructed; wipe the bottom of the drip tray and the cavity it sits in.
HEADS UP Don't try to bypass this by unplugging it—the reminder is stored in memory. You have to run the cycle.