Site index removes "www" from url and files (e.g., '/about') don't work with "www."
The following rules remove the www everywhere on your domain.
Put it in .htaccess file:

  RewriteEngine On
  RewriteBase /
  RewriteCond %{HTTP_HOST} ^www.yourdomain.com [NC]
  RewriteRule ^(.*)$ http://yourdomain.com/$1 [L,R=301]