Problem with file upload on edit page

Code:
function update()

    {    

    



    

      $content = array('title' => $_POST['title'],

                      'category' => $_POST['category'],

                    'description' => $_POST['description'],

                  'order' => $_POST['order']);

    

    if ($_FILES['myfile'] != NULL)

    {

        $config['upload_path'] = './includes/uploads/';

        $config['allowed_types'] = 'gif|jpg';

        $config['max_size'] = '1000';

        $config['remove_spaces'] = true;

        $config['overwrite'] = true;

        //$config['max_width']  = '400';

        //$config['max_height']  = '400';

        $this->load->library('upload', $config);    

        

        if( ! $this->upload->do_upload('myfile'))

        {

            echo $this->upload->display_errors();

            exit();

        } else

        {

        

            // Thumbnail

            $data = array('upload_data' => $this->upload->data());

          $temp=$this->upload->data(); 

          

          $thumb['image_library'] = 'GD2';

          $thumb['source_image'] = './includes/uploads/'.$temp['file_name'];

          $thumb['new_image'] = './includes/uploads/thumb/'.$temp['file_name'];

          $thumb['maintain_ratio'] = TRUE;

          $thumb['create_thumb'] = TRUE;

          $thumb['quality'] = '100';

          $thumb['height'] = '80';

          $thumb['width'] = '80';

      

          $this->load->library('image_lib', $thumb);

          $this->image_lib->resize();

          

           //making a thumbnail

            $this->image_lib->clear();

            

            //insert to the DB





            $content['file'] = $temp['file_name'];





        }



        $this->db->where('id', $_POST['id']);

        $this->db->update($this->table, $content);

      }





    }