validation file uploadin

Hello everybody
i am building a simple help system with codeigniter. and users can attachment files when response to a ticket.
But I do not know how to display error for users when uploading files has problem encountered in view tickets. please check my code. i really need your help

PHP Code:

public function show()
    {
        $show = array();
        $id = $this->uri->segment('3');
        $groups_id = $this->ticket_model->get_groups_id($id);
        $show['show_ticket'] = $this->ticket_model->show($id, $groups_id);

        foreach ($show['show_ticket'] as $show_value){
            $show_gorup_id = $show_value['department_id'];
            $create_by_id = $show_value['user_id'];
        }

        $show['show_ticket_comment'] = $this->ticket_model->get_reply($id);

        foreach ($this->aauth->get_user_groups() as $user_groups) {
            $user_groups_id = $user_groups->id;
        }

        if (($this->aauth->is_member('Admin')) ||($user_groups_id == $show_gorup_id) || ($create_by_id == $this->aauth->get_user_id())) {
            $this->template->load('ticket/show_ticket', $show);
        }else{
            echo 'Access Denied';
        }
    } 








public function reply()
    {
        $config['upload_path'] = './file_ticket';
        $config['allowed_types'] = 'gif|jpg|png|jpeg|pdf|doc|docx|txt';
        $config['max_size'] = 4000;
        $config['max_width'] = 11024;
        $config['max_height'] = 7168;
        $this->load->library('upload', $config);
        $this->upload->initialize($config);

       // if ( !$this->upload->do_upload('userfile')) {
         //   $error = array('error' => $this->upload->display_errors());
          //  $this->load->view('upload_form', $error);
           // return;
        //}

        $uploadData = $this->upload->data();
        $file = $uploadData['file_name'];


        $this->form_validation->set_rules('comment', 'Comment', 'required|trim');
        if ($this->form_validation->run() == FALSE) {
         //    $this->template->load('ticket/show_ticket',array('groups' => $ticket_add));
        //what code needs for display error here ?

        } else {
            $reply_ticket['ticket_comment_id'] = '';
            $reply_ticket['ticket_id'] = $this->input->post('ticket_id');
            $reply_ticket['user_id'] = $this->aauth->get_user_id();
            $reply_ticket['comment'] = $this->input->post('comment');
            $reply_ticket['create_date'] = now();
            $reply_ticket['file'] = $file;
            $insert_ticket_comment = $this->ticket_model->reply($reply_ticket);
            if ($insert_ticket_comment) {
                $show = array();
                $id = $this->input->post('ticket_id');
                $groups_id = $this->ticket_model->get_groups_id($id);
                $show['show_ticket'] = $this->ticket_model->show($id, $groups_id);

                redirect('ticket/show/'.$id);
            }
        }
    }