probleme d'installation

bonjour, après installation, j'ai cette erreur lorsque je me connecte à http://localhost/opacce :

Warning: require_once(Zend/Loader.php): failed to open stream: No such file or directory in C:\xampp\htdocs\opacce\library\startup.php on line 65

Fatal error: require_once(): Failed opening required 'Zend/Loader.php' (include_path='C:\xampp\htdocs\opacce;C:\xampp\htdocs\opacce/library;C:\xampp\htdocs\opacce/library/storm/src;C:\xampp\htdocs\opacce/library/storm/zf/library;C:\xampp\htdocs\opacce/library/digital_resources;C:\xampp\htdocs\opacce/library/templates;.;\xampp\php\PEAR') in C:\xampp\htdocs\opacce\library\startup.php on line 65

une idée ? merci