can't disable the plugin or theme editor

The main configuration file needs to be writable to harden the plugin and theme editors, and also the file must be accessible with at least read permissions. If you are not seeing an error message explaining why the hardening is not applied then there must be an issue with your site.

If you provide more information about your current configuration I can help you more. For the time being you can disable the plugin and theme editors adding this code in the main configuration file:

define("DISALLOW_FILE_EDIT", TRUE);