PHP XQueryLite problem

I'm having a problem with a PHP script that utilizes the XQueryLite object.  Here's the script source:

<?php

$artId = $_GET['artId'];

$testQuery= '{
     for $a in document("news.xml")//NEWS/ARTICLE
     where $a/@ID='.$artId.'
     return {$a}
}';

$query=stripslashes($testQuery);
include_once("class_xquery_lite.php");
$xq=new XqueryLite();
$xml=$xq->evaluate_xqueryl($query);
//print($result);
//$xml = get_xml_from_datasource();

$arguments = array(
  '/_xml' => $xml
);

$xp = xslt_create();
$result = xslt_process($xp, 'arg:/_xml', 'article.xsl',
                       NULL, $arguments);
echo $result;
xslt_free($xp);
?>


And here's the error XQueryLite is returning:

Warning: dump_node(): Object has to be a DomDocument Node in /u/web/wwwedc/class_xquery_lite.php on line 187

The error occurs when I call the xslt_process() function in the script.  Any ideas?