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:

which outputs xml just fine.

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!

$xsl=new DomDocument();

$xslt=new XSLTProcessor();

$xml=new DomDocument();




echo $results;