sh404SEF® uses default settings that should allow proper operation on most Apache servers. If you get up-front 404 errors on all your links, your SEF URL probably do not have a /index.php/ bit in them (for instance : www.mysite.com/index.php/my-page-title.html). So you probably have changed the default settings in sh404SEF® configuration, from "no .htaccess (/index.php/)" to something else. You should either : a/ switch back to "no .htaccess (/index.php/)" - preferred option, or b/ set up a ".htaccess" file in the root directory of your site. See next question about .htaccess files