Loaded MailChimp Widget plugin and now site won't load

I loaded the MailChimp plugin:
http://wordpress.org/extend/plugins/mailchimp-widget/

After activating it and getting this message:

Fatal error: Class ‘NS_Widget_MailChimp’ not found in /home/pistachi/public_html/wp-includes/widgets.php on line 324

domain: http://www.pistachiomedia.org

I cannot get into wp-admin, but I do have Coda and FTP access. I have contacted the service provider (Site 5) to make sure I don’t have to edit the .htaccess file

Any suggestions? I am pretty desperate here…

Thanks