[eluser]aquary[/eluser]
The joining condition is not good (for what the query is for). It'd works only if the news author and the modifier is the same person.
You have to separate the join into two parts.
Code:
$this->db->join('users', 'users.id = news.author', 'left');
$this->db->join('users modified_user', 'modified_user.id=news.modified_by', 'left')
Optionally, you may also have to change the select to choose the name of each person manually.
Code:
$this->db->select('news.*, news.id as news_id, news.created as created_on, users.name as author_name, modifier_users.name as modifier_name');