Hi Lucie,
Did you select "Only Continue Black & White Printing" on your MF726Cdw then print from your computer?
If you need immediate assistance and you're in the USA, please click http://Canon.us/ContactCF for our US-based support. If you're outside of the US, please click http://Canon.us/4xf7 for support options.
Did this answer your question? Please click the Accept as Solution button so that others may find the answer as well.