Activating pro version of wp smush

I recently purchased wpmudev and when i try to activate the pro version of wp smush it gives this error:
Fatal error: Cannot redeclare wp_smush_rating_message() (previously declared in /nas/wp/www/cluster-40300/playworld/wp-content/plugins/wp-smushit/wp-smush.php:73) in /nas/wp/www/cluster-40300/playworld/wp-content/plugins/wp-smush-pro/wp-smush.php on line 88