Display shows 'Empty waste container' even when the container is empty and reinserted.

User-level steps:

• Remove the waste container and clean it thoroughly, including any tabs or fins that interact with sensors.
• Clean the area inside the machine where the container slides in.
• Reinsert the container firmly until it clicks.

Technical inspection:

• Check the waste container presence microswitch or optical sensor for coffee residue, and clean carefully.
• Test the sensor with a multimeter and replace it if faulty.