This can occur for a variety of reasons. Try any of the following:
- If you have the POWERPACK/Productivity add-on installed, check to see if the capability edit_ticket_with_full_editor has been assigned to your role. If so, remove it. It means that the using the advanced editor for replies is incompatible with your installation.
- Add this to your wp-config.php file: define(‘CONCATENATE_SCRIPTS’, false );
- Check for the existence of a .htaccess file in wp-includes. If one exist, remove it or rename it temporarily to see if it fixes the issue. If it does you’ll need to get with your server admin to decide how to handle that file
- Check to see if any directive in any .htaccess file might be preventing access to executions in the wp-includes/js folder. Your host might also be preventing access to this folder.
- If all else fails do a google search for “wordpress editor loaded disabled”. Maybe one of the many suggestions there might help.