You’ve copied the source from some kind of dev tools, as far as I can see, so I can’t be 100% sure what your original source looks like but here is an issue nonetheless – the <ul>
element is not properly nested here:
<li><a href=""> Listing</a>
</li>
<ul>
<li><a href="modules.php?set=modules_products_listing"> Product Listing</a>
</li>
<li><a href="configuration.php?gID=8"> Order display</a>
</li>
</ul>
Should look like this:
<li><a href=""> Listing</a>
<ul>
<li><a href="modules.php?set=modules_products_listing"> Product Listing</a>
</li>
<li><a href="configuration.php?gID=8"> Order display</a>
</li>
</ul>
</li>
Fix this (all occurrences) and let me know if you still have any troubles.