Some Canon printers are able to print on CDs or DVDs, where you can put a printable CD or DVD into a tray and feed it to the printer.
During the printing process many users experience problems with different error messages and the result is that the CD tray is being rejected.

The first trick to solve this problem is to wait with inserting the CD tray into the printer until you get a message on the screen that tells you to insert the CD tray, otherwise the CD tray will be rejected by the printer because it’s not ready for it yet.
The second trick is to assist the CD tray after inserting it into the printer by lifting the rear end up approximately 5 - 10 mm, this will make the printer feed the CD tray correctly without rejecting it.