Docbook-xml, xsltproc, FO and xsltproc

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First of all, I apologize for the cross-post. But as the nature of my
question is not clear to me, I didn't know to which list to post. I hope
to fix my error once I know the good list.

Now, on with the question.

I have a docbook xml file that contains text in UTF-8 (my mother tongue
is spanish) and footnotes.
I generate (or at least attempt to) an fo rendition of the document
through the use of xsltproc and the corresponding xsl
((.*)/fo/docbook.xsl, both Norman Walsh's and Norman Walsh's +
sourceforge collaborators).

But xsltproc segfaults with the following message:

XPath error : Undefined variable
$ulink.footnotes != 0
                 ^
error: file /usr/share/xml/docbook/stylesheet/nwalsh/fo/footnote.xsl
line 94 element number
Failed to compile predicate

I don't have the exact message near me right now, but something similar
happened when I tried other xslt processors (name saxon and xalan), so
that makes me thing this problem is not tool-specific.

Xmllint seems to agree on the well-formedness and validity of the document.

Does that mean I can not have footnotes in docbook xml documents? What
about docbook sgml? May be the tools?

TIA :-)
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