Trying to allow my moderators permissions to use the Theme Editor and it's not working, tried to change permissions under Staff/Moderators/Edit and it took me to a 500 error page. Even removing all my moderators and deleting the group and re-adding it hasn't done anything to fix.

Please disable all 3rd party applications and test this again. If you are then still having issues, please let me know the name of the group or member you are trying to add that permission to