theme_links creates invalid identifier / html code

i have created primary and secondary menu links and saw many errors in the validator. As you can see the ID starts with numeric what isn't allowed.

HTML:

<ul class="links secondary-links"><li class="menu-166 first"><a href="/drupal6/" title="" id="166">Link 1</a></li>
<li class="menu-167 last"><a href="/drupal6/" title="" id="167">Link 2</a></li>
</ul>

Errors:

line 47 column 108 - Error: value of attribute "id" invalid: "1" cannot start a name
line 48 column 59 - Error: value of attribute "id" invalid: "1" cannot start a name