WWW vs. Non WWW

Pick www or non-www, then add the following code (see last) to wp-config.php with a slash at the end of /*toggle on/off*/ (like that) to activate the two lines following and then browse your site just a bit, then turn that back off and go to Dashboard > Settings > General and save what you have there. That should update your database to whichever you had selected, but I still also had to do a manual search via phpMyAdmin to find and edit a few places that had somehow been missed. Prior to doing that, however, use something like either of these first two bits of code in .htaccess (if you have .htaccess) to redirect all traffic of one type or the other to the other:

RewriteEngine On
RewriteBase /
# redirect all www. to non-www.
RewriteCond %{HTTP_HOST} ^www\.domainname\.com$ [NC]
RewriteRule ^(.*)$ http://domainname.com/$1 [R=301,L]
RewriteRule ^index\.php$ - [L]

RewriteEngine On
RewriteBase /
# redirect all non-www. to www.
RewriteCond %{HTTP_HOST} ^domainname\.com$ [NC]
RewriteRule ^(.*)$ http://www.domainname.com/$1 [R=301,L]
RewriteRule ^index\.php$ - [L]

<?php
/**
* The base configurations of the WordPress.
*
* @package WordPress
*/
/*-either-*/
/** @ root/wp-config.php: /*toggle on/off*
define('WP_HOME','http://domain.com');
define('WP_SITEURL','http://domain.com');
/*-or-*/
/** @ root/wp-config.php: /*toggle on/off*
define('WP_HOME','http://www.domain.com');
define('WP_SITEURL','http://www.domain.com');
/*-end-*/

I do not know enough about .htaccess to help you there, but that appears to be making everything go to http://www. So, I might try adding the non-www-to-www code just above that and see what happens.

If you do end up going into your database, here is the SQL code I used there:

UPDATE pref_options SET option_value = replace(option_value, 'http://www.mydomain.com', 'http://mydomain.com') WHERE option_name = 'home' OR option_name = 'siteurl';

UPDATE pref_posts SET guid = replace(guid, 'http://www.mydomain.com','http://mydomain.com');

UPDATE pref_posts SET post_content = replace(post_content, 'http://www.mydomain.com', 'http://mydomain.com');

UPDATE pref_postmeta SET meta_value = replace(meta_value,'http://www.mydomain.com','http://mydomain.com');

note: To make non-www into www, just switch 'http://www.mydomain.com','http://mydomain.com'); to 'http://mydomain.com','http://www.mydomain.com'); in all lines.

Also, change ‘pref’ to your own table_prefix.