htaccess / redirect problem with multisite

When I activated WP Multi-site to my existing blog, the instructions told me to change the site URL in the wordpress settings to a non-www prefix URL. The error I have is - when you visit the www version of the URL, it redirects you to the home page. For example:

http://www.marketeralliance.com/wp-admin/

vs

http://marketeralliance.com/wp-admin/

My htaccess file code is:

RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ - [L]

# add a trailing slash to /wp-admin
RewriteRule ^([_0-9a-zA-Z-]+/)?wp-admin$ $1wp-admin/ [R=301,L]

RewriteCond %{REQUEST_FILENAME} -f [OR]
RewriteCond %{REQUEST_FILENAME} -d
RewriteRule ^ - [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(wp-(content|admin|includes).*) $2 [L]
RewriteRule ^([_0-9a-zA-Z-]+/)?(.*.php)$ $2 [L]
RewriteRule . index.php [L]