The File Editor or Robots.txt modules are missing

This no longer applies to All in One SEO v4.0.

If you have activated either the File Editor module or Robots.txt module but they don't appear in the All in One SEO Pack sub menu then it's possible that you have disabled file editing in WordPress using the DISALLOW_FILE_EDIT or DISALLOW_FILE_MODS directives in your wp-config.php file - https://codex.wordpress.org/Editing_wp-config.php#Disable_the_Plugin_and_Theme_Editor