error/moodle/adminprimarynoedit
From MoodleDocs
The primary administrator account has some special restrictions to keep others administrators from making changes that could potentially impact the primary administrator. As a result, even a user with administrative privileges cannot change the user profile of the primary administrator. You must login as the primary administrator in order to make changes to the primary administrator's user profile. Otherwise, any administrative user could change the password of the primary administrator and he would be locked out.
