This error happens when the filament change function is triggered. This can happen by:
How to proceed?
Remove the old filament from the MMU unit and replace it with a new one. Click the option Load and select the desired filament position. You can select the one you previously used or a new position.
In case you need to eject the depleted filament out of the front of the MMU unit, select Eject. The Selector will move until the filament slot is free, and the filament will be ejected to the front so that you can pull it out easily.