fatal error when trying to active WP Smush

I get this error when I try to activate WP Smush - just started the free trial so I have no experience with using it...

Fatal error: Cannot redeclare i18n() (previously declared in /home/content/p3pnexwpnas07_data02/69/3188369/html/wp-content/plugins/wp-smushit/wp-smush.php:278) in /home/content/p3pnexwpnas07_data02/69/3188369/html/wp-content/plugins/wp-smush-pro/wp-smush.php on line 274