Error when www is added in front of WordPress Site Name

If you navigate to grategrlic.com without www in front of it, the site works fine, no error. If you include the www, you receive the following error on an all white screen:
Warning: Cannot modify header information – headers already sent by (output started at /home4/driskell/public_html/grategarlic.com/index.php:9) in /home4/driskell/public_html/grategarlic.com/wp-includes/pluggable.php on line 1178
Any help or guidance would be appreciated. I need to get this site up as soon as possible. No changes have been made to the code of the site and the installation has been taken back to the bare bones WP installation to no effect. I have also switched out to a standard theme and still receive the error.