So this should be:
<ul id="topmenu" class="sf-menu sf-navbar">
<% control Menu(1) %>
<li <% if LinkOrSection = section %>class="current"<% end_if %>><a href="$Link" >$MenuTitle</a>
<% if Children %>
<% if URLSegment = whats-new %>
<ul>
<% control Children %>
<li class="hidden"><a href="$Link" >$MenuTitle</a></li>
<% end_control %>
</ul>
<% else_if URLSegment = work-with-us %>
<ul>
<% control Children %>
<li class="hidden"><a href="$Link" >$MenuTitle</a></li>
<% end_control %>
</ul>
<% else %>
<ul>
<% control Children %>
<li class="$LinkingMode"><a href="$Link" >$MenuTitle</a></li>
<% end_control %>
</ul>
<% end_if %>
<% end_if %>
</li>
<% end_control %>
</ul>