Facebook php sdk function api（）退出脚本而没有Exception

I'm currently developing a game on Facebook and I'm trying to get userinformation via the php-sdk, after some starting problems i've managed to load the sdk, pick up a session stated in JS and retrieve the user id.

As soon as i try to call the api() function the php script stops, like i called exit, the output in the browser is just everything that happended befor the api() function.

When i get this script via the Apache HTTPClient in java i realise the server actually returns a 500 server error, without further descrition.

$config = array(
    'appId' => 'XX',
    'secret' => 'XXXX',
    'allowSignedRequest' => false,
);

$fb = new Facebook($config);

try{
    $ret = $fb->api('/me',"GET");
}
catch(FacebookApiException $e)
{
    echo "exception";
echo $e->getMessage();
}