I am trying to print labels using the rear tray on a canon mx870. I choose rear tray and it still will only try to print from the cassette. I was printing from it last week. Another computer printed to it since then. Other than that I don't know what else to do. It doesn't give me an option to choose labels only photo paper which is too much inch for the labels. I have tried to say I am using custom sized paper but even changing that has not helped. I took the paper out of the bottom cassette.