Canon S400 Reference Manual page 193

Check 1
Is the auto sheet feeder overloaded?
The number of sheets you can load in the auto sheet feeder depends on
the media you are using. The media does not feed correctly if you exceed
the prescribed number of sheets.
Check 2
Is the paper folded or curled?
To avoid misfeeds and paper jams, never load paper in the auto sheet
feeder that is folded, curled or wrinkled.
Check 3
Is the paper guide set correctly?
If the paper guide on the auto sheet feeder is not set correctly, the paper
does not feed straight or may jam in the printer. The paper guide must be
snug against the side of the stack and not too tight.
Number of sheets that can be loaded
Media Types You Cannot Use with the Printer
Troubleshooting - Paper Jams or Does Not Feed
Paper skewing during feeding
193