Answer: The waste ink in the waste ink tank have reached a certain amount (80%).

Reset the waste ink in the waste ink tank by replacing the waste ink tank or discarding
the waste ink by pulling it into alternate container. Once resetting the waste ink on
the machine, the warning message [Check waste ink] will go off.
If keep operating the machine by resetting the waste ink yet in fact there are good
volume remained in the tank, it will be eventually over-floated.
Click here to see how to discard waste ink in the waste ink tank.
[How to reset the waste ink]

(1) Go to MENU -> MAINTENANCE -> REPLACE WasterInkTank,
　　and then press [ENTER] key.

(2) Press [ENTER] key twice while the machine shows Waste ink level.

*When resetting the waste ink with the remaining waste ink is less than 80%,
　then operate the ▲(UP) key to change the level more than 80%, and press
　the [ENTER] key to reset it.
　Also you can operate ▲(UP) or ▼(DOWN) keys to register the actual waste ink.