Deprive,

 

Your code works for me in the following example:

 

 

<li><a href="ajaxpage('about_us.html','content');">About Us</a>
<ul>
    <li><a href="ajaxpage('au_volunteers.html','content');">Volunteers</a> </li>
</ul>
</li>

 

If it works for you as well, can you ask your developer download the latest build of version 6.0?

 

Thanks.