Ensure that Norman Walsh's DocBook XSL stylesheets, available at http://docbook.sourceforge.net/projects/xsl/, are installed and are added to your XML catalog file (see http://www.xmlsoft.org/catalog.html for more information on catalogs).
Ziurtatu Norman Walsh-en DocBook XSL estilo-orriak (http:docbook.//sourceforge.net/projects/xsl/ helbidean erabilgarri), instalatuta daudela eta zure XML katalogo-fitxategian gehituta (ikus http://www.xmlsoft.org/catalog.html katalogoei buruzko informazio gehiago lortzeko).