Yes, I am sure that the header_php.php is in the includes/modules/pages/product_reviews_write

I do see the warning when Enable Product Reviews By Guests is set to 0 (off). Then it says you must log in. However, when set to 1 to allow, it still redirects to the login/account creation page but does not show the warning. Does not allow gusts to write even though Enable Product Reviews By Guests is set to 1