The problem is that the wrong type of ink will melt when the laser printer is fusing the toner to the paper. This melted ink will cause a build up on the upper fuser roller. This roller is a Teflon coated roller. Teflon is a no stick surface and once the ink from the letterhead sticks to it, the roller picks up toner and will re-deposit the toner on your page causing a repetitive mark down the page. The mark is usually the exact copy of a part of that same page.
Most laser printers provide error messages when they malfunction.
On the Canon based printers there is usually a number associated with the message. It is helpful if you write down this number and the message. Some error messages allow you to continue with the print process while other ones demand that you pay some attention to the printer. We have found a simple action that is very helpful when working with electronic devices. Pay attention to the order you turn things on.