无法访问与您的字段名称对应的错误消息

我有一个回调函数，check_captcha它查看$row是==0还是== 1(此信息是从sql查询的(。

问题是我无法从$self->form_validation->set_rule('captcha', 'call_back_check_captcha')调用它，因为我的函数接受一个$row变量。我现在调用它的方式收到"无法访问"错误消息。我怎样才能做到这一点？

function check_captcha( $row)
{
    if($row ==0)//didnt find any
    {
        $this->form_validation->set_message('captcha', 'text dont match captcha');
        return FALSE;
    }
    else
    {
        return TRUE;
    }
}

function create_member() 
        {   
            $past = time() - 7200; 
        $this->db->query("DELETE FROM captcha WHERE captcha_time <".$past);                 
        $sql = "SELECT COUNT(*) AS count FROM captcha WHERE word =? AND ip_address =?";     
        $binds = array($_POST['captcha'], $this->input->ip_address(), $past);
        $query= $this->db->query($sql, $binds);
        $row = $query->row(); //row query rows : if it found an entry =1 
            $self->check_captcha($row->count);
        //VALIDATIONS
        $this->form_validation->set_rules('first_name', 'First Name', 'trim|required');
        $this->form_validation->set_rules('last_name', 'Last Name', 'trim|required');      
        $this->form_validation->set_rules( 'email_address', 'Email Address', 'trim|required|valid_email|unique[user.email_address]');
        $this->form_validation->set_rules('username', 'Username', 'trim|required|min_length[4]|unique[user.username]');
        $this->form_validation->set_rules('password', 'Password', 'trim|required|min_length[4]|max_leng[32]');
        $this->form_validation->set_rules('password2', 'Password Confirmation','trim|required|matches[password]');
        if(!$_POST['captcha']){
        $this->form_validation->set_rules('captcha', 'Captcha','trim|required');}else{
        $this->form_validation->set_rules('captcha', 'Captcha', 'callback_check_captcha');}
        if($this->form_validation->run()==FALSE)
        {   //this -> to the curr obj(UserController) && registraion() points to the the function in controller
            $this->registration();  //reloads reg page so they can fill out right stuff
        }
        else