the system is designed to expect at least one submenu item.
if you dont want any submenu items, you will need to edit the webassist/plugins/main_menu/menu.php file and change this code:
<ul class="level-1">
<?php
echo($WACustomPages->Body);
?>
</ul>
to:
<!--<ul class="level-1">
<?php
echo($WACustomPages->Body);
?>
</ul>-->
this will comment it out, or you can delete it completely.