Internet Explorer unsupported get request

I got a big problem in IE (only IE, FF etc works great).

I got a canvas page: xyz.de/gewinnspiel.php?register=1. In IE I get the following error:

FacebookApiException: Unsupported get request. in Facebook->_graph()

Does anybody have an idea?

---

IE8

$facebook = new开发者_StackOverflow Facebook(array(
    'appId' => $app_id,
    'secret' => $app_secret,
    'cookie' => true
    ));

$loginuser = $facebook->getUser();

$userInfo           = $facebook->api("/$loginuser");

the $userInfo triggers the error...