Doctrine cannot redeclare class Annotation - php

Question

i've got my bootstrap
<?php
use Doctrine\ORM\Tools\Setup;
use Doctrine\ORM\EntityManager;
// Log Filename
define ('LOG_FILENAME', 'clicktocall-'.date("Ymd").'log');
$loader = require "vendor/autoload.php";
// Doctrine parser
Doctrine\Common\Annotations\AnnotationRegistry::registerLoader(array($loader, 'loadClass'));
// Create a simple "default" Doctrine ORM configuration for Annotations
$isDevMode = true;
$config = Setup::createAnnotationMetadataConfiguration(array("./src/acme"), $isDevMode);
// Database configuration parameters
$dbParams = array(
'driver' => 'pdo_mysql',
'host' => 'localhost',
'user' => 'xxx',
'password' => 'yyy',
'dbname' => 'zzz',
);
// Obtaining the entity manager
$em = EntityManager::create($dbParams, $config);
// Setting Logger Monolog
$Logger = new \Monolog\Logger('CTLogger');
$Logger->pushHandler(new \Monolog\Handler\StreamHandler('./log/'.LOG_FILENAME, \Monolog\Logger::INFO));
When i'm trying to execute
vendor\bin\doctrine orm:schema-tool:update --force
I obtain this message
Fatal error: Cannot redeclare class Doctrine\ORM\Mapping\Annotation in E:\www\acme\vendor\doctri
ne\orm\lib\Doctrine\ORM\Mapping\Annotation.php on line 22
I'm just using Doctrine bundle.
Any idea?
Thanks a lot
[Edit]
I've found that the problem is caused by
Doctrine\Common\Annotations\AnnotationRegistry::registerLoader(array($loader, 'loadClass'));
I use this row to parse the annotations for the symfony\validator bundle, without this the validation doesn't work...