Custom Titlepage Error: Missing URI in namespace declaration

Hello,

following Bob Stayton's guidelines in "Chapter 11. Print customization 
examples" I get the following error when applying the customized 
stylsheet to a Docbook document:

Error reported by XML parser: Missing URI in namespace declaration: 
xmlns:ns1
   URL:    file:/KM/usr/ziegler/LEDA/Tutorial/XSLT/mytitlepages.xsl
   Line:   152
   Column: 46
Error reported by XML parser: undeclared name prefix in: ns1:keep-with-next
   URL:    file:/KM/usr/ziegler/LEDA/Tutorial/XSLT/mytitlepages.xsl
   Line:   152
   Column: 116

The corrsp. line 152 in mytitlepages.xsl look like this:

<fo:block xmlns:fo="http://www.w3.org/1999/XSL/Format" xmlns:ns1="" 
xsl:use-attribute-sets="article.titlepage.recto.style" 
ns1:keep-with-next="always" ns1:font-size="24.8832pt" 
ns1:font-weight="bold">

Here's what I did:

1) I copied

fo/titlepage.templates.xml

to a local directory.

2) Added the line

  <releaseinfo/>

  into
<t:titlepage t:element="book" t:wrapper="fo:block">
   ...
  <t:titlepage-content t:side="verso">
   ...

3) Created my own titlepage stylesheet:

xsltproc  -output  mytitlepages.xsl 
/KM/usr/ziegler/DocBook/docbook-xsl-1.60.1/template/titlepage.xsl
titlepage.templates.xml

4) Inluded it into my FOP-stylesheet.

<xsl:include href="mytitlepages.xsl"/>

Greetings,
Joachim

-- 
Joachim Ziegler                       Stuhlsatzenhausweg 85
Max-Planck-Institut für Informatik    66123 Saarbrücken
Email:           Germany