Getting this error message so cannot activate WP Smush Pro plug in.

Getting this error message so cannot activate plug in WP Smush Pro. How to fix? Thank you!
Using WordPress 4.4.1 running up-to-date Enfold theme.

message:
Plugin could not be activated because it triggered a fatal error.

Fatal error: Cannot redeclare wp_smush_rating_message() (previously declared in /home3/meditay8/public_html/wp-content/plugins/wp-smushit/wp-smush.php:73) in /home3/meditay8/public_html/wp-content/plugins/wp-smush-pro/wp-smush.php on line 68