How are you referencing the DTD file or URL?
URL. In particular, with a PUBLIC doctype declaration like this:
<?xml version="1.0" ?>
<!DOCTYPE article PUBLIC "-//OASIS//DTD DocBook XML V4.1.2//EN"
"http://www.oasis-open.org/docbook/xml/4.1.2/docbookx.dtd";><article ... > ... </article>
Sixten
