php – codeigniter表单验证错误消息不显示

$this->form_validation->set_rules('bookCategoryId','Book SubCategory Id','trim|required');
        $this->form_validation->set_rules('bookSubCategoryId','trim|required');
        $this->form_validation->set_rules('bookSubCategoryName','Book SubCategory Name','trim|required');
if ($this->form_validation->run() == FALSE) {
        /* Load Model */
        $this->load->model('book_category');

        /* Get Categories */
        $template_data['mainContentData']['book_categories'] = $this->book_category->get_all_categories();

        /* set view page to be called  */
        $template_data['mainContent'] = 'admin_add_book_subcategory';

        /* Load Template */
        $this->template($template_data);
    }

如果我排除这两行,我的表单工作正常

/* Load Model */
        $this->load->model('book_category');

        /* Get Categories */
        $template_data['mainContentData']['book_categories'] = $this->book_category->get_all_categories();

比我的验证显示错误.我不知道问题出在哪里？