Canon S400 Reference Manual page 171

Check 1
Are you using the paper size specified in the Page Size setting?
If the size of the paper loaded in the printer does not match the Page Size
setting in the printer driver, part of each page may not print.
Check the Page Size or Paper Size setting. If it does not match the size of
the paper you are using, select the correct size from the pull-down list.
The Page Size or Paper Size can be found at the following location:
Page Layout tab
Windows
Page Setup dialogue box
Macintosh
Note Set the same Page Size setting for the application program and the printer
driver.
Select the Page Size that matches the Page Size setting in the application
program.
Check 2
Are the computer and printer securely connected?
Check the connection of the printer cable at the computer and printer. A
loose connection can cause losing part of a print job.
Last part of print job not printing
Troubleshooting - Printout is Unsatisfactory 171