Canon PIXMA MX850 Series Quick Start Manual page 159

Cause
Document Jams in the ADF (Document
Output Slot).
If the document is jammed in the Document Output Slot, open the Document
Output Slot as shown in the figure below and pull out the document.
When rescanning the document after clearing the error, rescan it from the
first page.
If you cannot remove the document or the document tears inside the machine,
or if the document jam error continues after removing the document, contact
your Canon service representative.
Action
Troubleshooting 155