Fixing Unit Error Turn the printer off. If a USB cable is connected, turn the computer off, and then disconnect the USB cable from the printer. Unplug the power plug from the AC power outlet.
This error may also appear as the similarly worded "App Name" can't be opened because it was not downloaded from the Mac App Store." depending on the security settings on your computer. A sample of the error is shown below:
Precautions when Replacing Toner Cartridges Note: About the power of the printer You can replace the toner cartridges either when the power of the printer is turned on or when it is turned off.
Should you smell something burning, immediately turn OFF the machine, unplug the power plug from the AC power outlet, and contact your local authorized Canon dealer or the Canon help line at 800-652-2666 (800- OK-Canon). Continued use may lead to a fire or electrical shock.