working with xml from a php file for xsl transformations

I have a couple of files where I output xml based upon URI parameters passed into a PHP file. So I end up getting urls like this: menu_render.php?menu_id=4&format=xml which outputs xml just fine to a web browser but doesn't seem to work for a server. The problem I'm having is that I'd like to be able to open this file and then transform it via a stylesheet like below. Unfortunately, it gives me the following error: Warning: I/O warning : failed to load external entity "menu_render.php?menu_id=4&format=xml" in... I thought I was able to so this before. Does anybody know what I'm doing wrong. Help! Do you think it's a permissions issue? Code: //works ok $xsl=new DomDocument(); $xsl->load('xsl_arc.xsl'); //works ok $xslt=new XSLTProcessor(); $xslt->importStyleSheet($xsl); $xml=new DomDocument(); //neither of these work //$menu=file_get_contents(urlencode('menu_render.php?menu_id=4&format=xml')); $xml->load('menu_render.php?menu_id=4&format=xml'); //this will load ok if just a scrape of the above //$xml->load('menu.xml'); $results=$xslt->transformToXml($xml); echo $results;