rules2 error

rules1
$this->form_validation->set_rules('npm', 'npm', 'trim|required|is_natural|min_length[9]|max_length[9]|is_unique[daftar_mhs.npm]',
                        array('required'   => 'Kolom %s harus di isi!',
                              'is_natural'=> 'Isi hanya angka!',
                              'min_length' => 'Min. 9 karakter..',
                              'max_length' => 'Max. 9 karakter..',
                              'is_unique'  => '%s ini sudah ada!')
tabel1
UNIQUE KEY `npm` (`npm`)

rules2
$this->form_validation->set_rules('kamar', 'kamar', 'trim|required|is_unique[kamar_ikhwan.kamar]',
            array('required'   => 'Kamar harus di isi!',
                   'is_unique' => '%s ini sudah ada!'));
tabel2
UNIQUE KEY `kamar` (`kamar`)