A black bar or line appears on the edge of the paper when viewing the file, but does not appear when printed. The bars will appear to change sides from page to page.
These bars indicate the bound edge of a duplexed (printing on both sides of the paper) document. They will only appear when viewed, and not when printed.
To resolve this issue:
If you wish to remove these indicators, add the following ICS command to your ini file: ICSX=gui displayduplex disable.
You can learn how to use the ini file here.