XSL-question: What does "Namespace prefix fo is not defined" mean ?

Hi,

I have some trouble converting a docbook xml document to fo. I get
the warning:


:587; make one.fo
SGML_CATALOG_FILES=/etc/sgml/catalog xsltproc --catalogs \
--maxdepth 999 \
 --xinclude --output one.fo print.xsl one.xml
print.xsl:63: warning: Namespace prefix fo is not defined
   <fo:basic-link xsl:use-attribute-sets="xref.properties">


Where print.xsl looks like

<?xml version='1.0'?>
<xsl:stylesheet xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
                version="1.0">
<xsl:import href="/usr/share/sgml/docbook/stylesheet/xsl/nwalsh/fo/profile-docbook.xsl"/>
<xsl:import href="J.Biol.Chem.Mbfr.fo.xsl"/>
[..]
<!-- ulinks only the first time -->
<xsl:template match="ulink[preceding::ulink/@url=./@url]">
   <fo:basic-link xsl:use-attribute-sets="xref.properties">
   ^^^
   this is the offending line
[..]


I thought that I had all that is needed in the header of print.xsl. Am I 
missing something in order to comply with the warning ?

Thanks in advance,
  Marc Baaden

-- 
 Dr. Marc Baaden  - Institut de Biologie Physico-Chimique, Paris
 mailto:      -      http://www.marc-baaden.de
 FAX: +49 697912 39550  -  Tel: +33 15841 5176 ou +33 609 843217