Cannot Activate Mush Pro

I keep getting this error message when I try to activate Mush Pro:

Fatal error: Cannot redeclare get_plugin_dir() (previously declared in /public_html/uponthepoint.com/wp-content/plugins/wp-smushit/wp-smush.php:118) in /public_html/uponthepoint.com/wp-content/plugins/wp-smush-pro/wp-smush.php on line 116

Full directory path edited by staff.