Images / CSS fail to load when using www version of site.

This can be caused by the web browser 'single origin policy' please try adding the following .htaccess rules  at the top of a file called .htaccess in the htdocs folder for the domain

#Force non-www:

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