PHP XML string parsing returns "Trying to get property of non-object"

Im trying to export some data from here (XML)

e.g and For example i'm trying to get the by using this code:

$xml = simplexml_load_string($response);
$results = $xml->Iteration[0]->{'Iteration_query-def'};

The thing is that returns the Notice written in post's title.

Am i loosing something in the path of XML file ?

Thank you.