Problema con inclusione di una funzione.

[lyllo]

sto provando a creare dei thumbnails dopo che l'utente invia le sue immagini in rete.
ho trovato una funzione qui sul sito:

<?php

  /************************************************************\
  *
  *    Basic Thumbnail Generator Copyright 2007 Derek Harvey
  *         [url]www.lotsofcode.com[/url]
  *
  *    This file is part of Basic Thumbnail Generator.
  *
  *    Basic Thumbnail Generator is free software; you can redistribute it and/or modify
  *    it under the terms of the GNU General Public License as published by
  *    the Free Software Foundation; either version 2 of the License, or
  *    (at your option) any later version.
  *
  *    Basic Thumbnail Generator is distributed in the hope that it will be useful,
  *    but WITHOUT ANY WARRANTY; without even the implied warranty of
  *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  *    GNU General Public License for more details.
  *
  *    You should have received a copy of the GNU General Public License
  *    along with Basic Thumbnail Generator; if not, write to the Free Software
  *    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
  *
  *
  \************************************************************/

  require_once 'thumbnail.class.php';    
  $thumbnail = new thumbnail;
  
  if (!empty($_REQUEST['submit']))
  {
      $tmp = $_FILES['uploaded_file']['tmp_name']; 
      $org = $_FILES['uploaded_file']['name'];
      
      if ($tmp)
      {
          $directory = 'uploads'; // Upload files to here.
          $prefix = 'uploaded_'; // Filename prefixes
          
          // Upload all image files
          $lrgImage = $thumbnail->generate($tmp, $org, $directory, $prefix.'lrg', 300); // large file
          $medImage = $thumbnail->generate($tmp, $org, $directory, $prefix.'med', 200); // medium file
          $smlImage = $thumbnail->generate($tmp, $org, $directory, $prefix.'sml', 100); // small file
          
          if ($smlImage && $medImage && $lrgImage) // If all files are ok
          {
              $info = '
        <fieldset>
          <legend>Files uploaded successfully</legend>
          [img]'.$lrgImage.'[/img]
          [img]'.$medImage.'[/img]
          [img]'.$smlImage.'[/img]
        </fieldset>

        ';
          }
      }
      else
      {
          $info = '

No file selected</p>';
      }
  }
  
?>

che richiamo in un'altra pagina:

require_once('thumbnail.class.php');
$t = $_FILES["file$k"]['tmp_name'];
$sz = $_FILES["file$k"]['size'];
$n  = $_FILES["file$k"]['name'];
$dest = "../img/immagini/";
$smlImage = $thumbnail->generate($t, $n, $dest."/TB", 'TB_'.$n, 100); 

ma ricevo questo messaggio di errore: Fatal error: Call to a member function on a non-object in C:\WM\www\galleria\spt\add_imgs.php on line 50

mi sapete spiegare dove sbaglio?
grazie.