Diagnosis
Yeah, this one's common. The waste ink absorber pad inside the printer is at or near its estimated capacity limit. It's a maintenance part designed to catch excess ink from cleaning cycles.
How to Fix It
You need to reset the waste ink counter. On this model, you enter a service mode: With the printer on, press and hold the 'Go' (triangle) button for about 10 seconds until all the LEDs light up. Then press the 'Go' button 9 times. The printer will reset the counter and restart. This clears the message so you can print again.
If That Didn't Work
If the message returns very quickly, the physical waste ink pad might actually be saturated. You'll need to open the printer to check it and potentially replace the pad, which is a more involved repair.
Heads Up
Resetting the counter doesn't empty the physical pad. If ink starts leaking from the bottom of the printer, that's the pad overflowing, and you need to stop using it and replace the pad immediately to prevent a mess and damage.