Can't activate smush pro plugin - fatal error

Hi
I got this error message after clicking 'activate'.
Fatal error: Cannot redeclare wp_smush_rating_message() (previously declared in /home1/suvalsky/public_html/wp-content/plugins/wp-smushit/wp-smush.php:73) in /home1/suvalsky/public_html/wp-content/plugins/wp-smush-pro/wp-smush.php on line 88

Please can you help?
thx! Esther