Thanks for your reply.
I had placed the backend pages in an Admin folder and the public pages are in the main folder of the website.
So for my public pages the menu.php coding needs to be
<?php require_once("CSSMenuWriter/cssmw_content/menu.php"); ?>
while the backend pages in the Admin folder in order to show no error should be
<?php require_once("../CSSMenuWriter/cssmw_content/menu.php"); ?>
How should I solve this issue? If I change the menu.php for one then I'll get an error on the other. I thought my DA backend pages/tables needed to be in a separate folder but then I have this issue with the menu writer.