[Plugin: BigMailChimp] Fatal Error after installing Bigmailchimp

Fatal error: Class ‘MCFormWidget’ not found in /home/content/44/9317044/html/childsleepinstitute/wordpress/wp-includes/widgets.php on line 324

Tried using the add plug-in within WordPress, and also manually copying the files.

http://wordpress.org/extend/plugins/bigmailchimp/