Mysql 在dbal中关闭语句时出错

在我的silex web应用程序中，我有以下功能：

function obtener_visible($conn, $articulo, $wid)
{
    $q= $conn
        ->prepare('call vn2008.article_visible_single(?, ?)');

    $q->execute(array(0 => $wid, 1=>$articulo));

    $result = $q->fetch(); 

    $conn->close();

    return $result['suma'];       
}

但当我调用此函数时，我收到以下错误：

[Wed Oct  1 07:47:01 2014] PHP Warning:  obtener_visible(): Error occurred while closing statement in /home/nelo/web/silex/almacen.php on line 0    
[Wed Oct  1 07:47:01 2014] PHP Stack trace:    
[Wed Oct  1 07:47:01 2014] PHP   1. {main}() /home/nelo/web/silex/index.php:0    
[Wed Oct  1 07:47:01 2014] PHP   2. Silex\Application->run() /home/nelo/web/silex/index.php:38    
[Wed Oct  1 07:47:01 2014] PHP   3. Silex\Application->handle() /home/nelo/web/silex/vendor/silex/silex/src/Silex/Application.php:481    
[Wed Oct  1 07:47:01 2014] PHP   4. Symfony\Component\HttpKernel\HttpKernel->handle() /home/nelo/web/silex/vendor/silex/silex/src/Silex/Application.php:504    
[Wed Oct  1 07:47:01 2014] PHP   5. Symfony\Component\HttpKernel\HttpKernel->handleRaw() /home/nelo/web/silex/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/HttpKernel.php:61    
[Wed Oct  1 07:47:01 2014] PHP   6. call_user_func_array() /home/nelo/web/silex/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/HttpKernel.php:117    
[Wed Oct  1 07:47:01 2014] PHP   7. {closure:/home/nelo/web/silex/index.php:18-22}() /home/nelo/web/silex/vendor/symfony/http-kernel/Symfony/Component/HttpKernel/HttpKernel.php:117    
[Wed Oct  1 07:47:01 2014] PHP   8. executeFacade() /home/nelo/web/silex/index.php:20    
[Wed Oct  1 07:47:01 2014] PHP   9. Verdnatura\Almacen\obtener_articulo->execute() /home/nelo/web/silex/facade.php:28    
[Wed Oct  1 07:47:01 2014] PHP  10. obtener_visible() /home/nelo/web/silex/almacen/obtener_articulo.php:56

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有人能帮我解决这个错误吗？

你确定你的数据库管理器与

call

stations兼容吗？是的，我的数据库管理器是mysqli