Canon LBP7210Cdn Manual page 262

IMPORTANT
Be sure to align the paper guides with the width of the paper.
If the paper guides are too loose or too tight, this may result in misfeeds or paper jams.
Hold down the paper, then set it under the hooks (A) on the paper guides.
Make sure that the paper stack does not exceed the load limit mark lines (B).
IMPORTANT
Do not load the paper stack which exceeds the load limit mark lines.