the require once paths to the menu writer folder, i can say exactly what the path should be, that dfepends on the how the folder are configured.
If you have a page at:
admin/pagename.php
and the CSSMenuWriter folder is at the same level as the admin folder, then the require path in the admin/pagename.php file should be:
require_once("../CSSMenuWriter/cssmw_content/menu.php");