Footnote Problem

I've include footnotes in my document like this:
<para>...Modelica <footnote><para>Modelica is a registered 
...</para></footnote>...</para>

In the generated HTML-Output I get a Link after Modelica to the 
footnote, but the
Link doesn't work. If I look at the end of the HTML-File the footnote is 
there, but
without a Linklabel back to the text.

What did I make wrong?

regards Melanie