Problem with DTD (New User)

I am working through the xampl.xml created by converting BibTeX's
xampl.bib, and trying out all the buttons

Language environment is UTF-8
Emacs is 21.3.1 as supplied in Red-Hat Fedora Core 2

So far as I know, the underlying mode is nxml-mode-20041004
It is supposed to be auto-loaded by my .emacs file

When I query anything under the DTD button, I get the following

/usr/share/sgml/docbook/sgml-dtd-4.1-1.0-24/catalog line 2 col 22 entity atype
/home/pierre/projects/Bibulus/bibulus.dtd line 36 col 26 entity BIBLIO
/home/pierre/projects/Bibulus/xampl.xml line 2 col 37 
Name expected; at: :lang NMTOKE

I have a feeling that sgml-dtd-4.1-1.0-24 shouldn't be in there at all, 
but I don't know what is importing it and why?

Pierre MacKay