top level categories cannot be closed, there is really no way to make that work. Only subcategories that have additional subcategories can be closed by default.
you may want to make your top level category more of a header, then add the main categories under that and subcategories to the main category:
Products
-category1
--cat1 subcat1
--cat1 subcat2
-category2
--cat2 subcat1
--cat2 subcat2
also, on the webassist/plugins/side_menu/nested_accordion/sidemenu.php page, find the following line:
<script type="text/javascript" src="functions.js"></script>
and change it to:
<script type="text/javascript" src="../accordion/js/accordion.js"></script>
<script type="text/javascript" src="functions.js"></script>