How does the Dymo 550 label sensor work, and what can interfere with its function, leading to this error?

The Dymo 550's label sensor is typically an optical sensor that detects the presence of labels by sensing the gap between each label. Dirt, dust, or debris on the sensor can interfere with its ability to 'see' the labels. Using incorrect label types (e.g., rolls that are not recognized), or labels that are damaged or poorly manufactured, can also cause the sensor to malfunction. Finally, ambient light conditions are not expected to interfere with the operation, but a very bright light source directed into the sensor is a very rare cause.