Class 'FCKeditor' not found

I installed FCKeditor often on different versions of PHP servers, 4 or 5.

But this time I get the following error message:
Fatal error: Class 'FCKeditor' not found in /home/www/vhosts/csmota.qc.ca/httpdocs/graphinet/add_modif_sections.php on line 118

The PHP version is 5.0.4.

Do you know where is the mistake?

<?php include("fckeditor/fckeditor.php"); ?>

<?php
$oFCKeditor = new FCKeditor('contenu');
$oFCKeditor->Config["CustomConfigurationsPath"] = 'fckconfig_graphinet.js';
$oFCKeditor->BasePath = 'fckeditor/';
$oFCKeditor->Value = $contenu;
$oFCKeditor->Width = '453' ;
$oFCKeditor->Height = '400' ;
$oFCKeditor->Create();
?>

Thanks for your help!