Canon Mk2500 User Manual page 133

If you feed the label tape excessively in the reverse direction, the leading edge of the label
tape enters the cassette. Refer to Note, "What to do if the label tape becomes stuck inside
the cassette" ( page 38).
The ribbon of the ribbon cassette can slacken when it is fed reverse. Open the cover and
check whether the ribbon is slack. If it is slack, take up the slack.