I am getting error due to the od: in the xml file. This maybe your problem.
May I offer an easier method, simplexml. Remove both od: and this does what you want
$xml = simplexml_load_file("PageBox.xml"); // I made your code into a file named People.xml
$i = 0;
foreach ($xml->Page->PageBox as $PageBox)
if($PageBox[$i]->attributes()->BoxType == "TrimBox")
echo "The Width you seek is: ".$PageBox[$i]->attributes()->Width . "<br />";