As mentioned already xpath will fail is the default namespace 'xmlns' is used like in:
<?php
$xmlstring = $string = <<<XML
<?xml version="1.0" encoding="UTF-8" standalone="yes"?>
<workbook xmlns="http://schemas.openxmlformats.org/spreadsheetml/2006/main">
<fileVersion appName="xl" />
</workbook>
XML;
?>
xpath cannot search through the xml without explicitly specifying a namespace.
There are 2 options :
1. rename the 'xmlns' into something else to trick xpath into believing that no default namespace is defined.
2. register a string as the default namespace and use that string in all your queries. Unfortunatly, an empty space will not work.
No other option currently exist until XPath2.0 becomes the default library.