Problem using link with xlink:href with htmlhelp

Hello,

I try to generate a windows help file using htmlhelp. Everything worked
until i wanted to introduce an external link. When i inserted '<link
xlink:href="http://www.hzd.de">www.hzd.de</link>' in my DokBook, i also
had to add 
'<book lang="de"
	xmlns="http://docbook.org/ns/docbook"
	xmlns:xlink="http://www.w3.org/1999/xlink" >'.

Now generating HTML, XHTML and PDF works fine. But htmlhelp produces the
following error:

C:\HeWoG\Hilfe\XML>java  com.icl.saxon.StyleSheet
Anwenderhandbuch\Anwenderhandbuch.xml
../docbook-xsl-1.71.0/htmlhelp/htmlhelp.xsl use.extensions=1
No template matches book.
No template matches info in book.
No template matches org in info.
No template matches orgname in org.
No template matches adress in org.
No template matches street in adress.
No template matches city in adress.
No template matches postcode in adress.
No template matches link in adress.
No template matches country in adress.
No template matches email in org.
No template matches title in book.
No template matches subtitle in book.
Writing ../HTMLHelp/Handbuch.tmp/htmlhelp.hhp
Writing ../HTMLHelp/Handbuch.tmp/toc.hhc

Then no html files are generated. Only htmlhelp.hhp and toc.hhc are
generated.
When I strip the xmlns declarations (just '<book lang="de">') and the
link, the helpfile will be produced.

I use docbook-xml-4.5 together with docbook-xsl-1.71.0 and saxon 6.5.5.

This is my (simplified) docbook:
<?xml   version="1.0" encoding="UTF-8"?>
<!DOCTYPE book SYSTEM "..\..\docbook-xml-4.5\docbookx.dtd"> 
<book lang="de"
	xmlns="http://docbook.org/ns/docbook"
	xmlns:xlink="http://www.w3.org/1999/xlink" >
	<info>
	  <org>
	    <orgname>Hessische Zentrale f&uuml;r
Datenverarbeitung</orgname>
	    <adress>
		<street>Mainzer Strasse 29</street>
		<city>Wiesbaden</city> <postcode>65185</postcode>
		<link xlink:href="http://www.hzd.de">www.hzd.de</link>
		<country>Germany</country>
	    </adress>
	    <email></email>
	  </org>
	</info>
	<title>HeWoG-Web Anwenderhandbuch</title>
	<subtitle>Hessisches Wohngeldverfahren</subtitle>
</book>

Kind regards
Thomas Fehling