XSLT failing when DOCTYPE declaration present

I'm using the xslt capabilities in PHP 4.2.2 and running into an odd problem. I'm transforming an XML document which has a DOCTYPE declaration referencing an external DTD. <!DOCTYPE RootNode SYSTEM "http://my.host.org/foo.dtd"> When I have xslt_process() attempt to transform the XML document, with an XSL document I provide, it fails. These are the errors I get back from xslt_error() & xslt_errno. error: XML parser error 4: not well-formed (invalid token). errno: 2 If I remove the DOCTYPE declaration from the XML, xslt_process() has no problem transforming the XML. If I change the DOCTYPE declaration to: <!DOCTYPE RootNode SYSTEM "file:///path/to/docroot/foo.dtd"> then xslt_process() has no problem transfoming the XML. However, I need to make this work with the external DTD reference being to some other host (http://other.my.host.org/foo.dtd). Has anyone gotten this to work properly, have any insight into the error information above, or know what I might have to do differently? THX, ~Chris