Fatal error upon activation

Installed but got an error trying to activate it on a Network installation. Site uses PHP 5.2.

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

Warning: require_once(__DIR__/vendor/autoload.php) [function.require-once]: failed to open stream: No such file or directory in /home/***/public_html/***.ca/wordpress/wp-content/plugins/php-compatibility-checker/wpengine-phpcompat.php on line 15

Fatal error: require_once() [function.require]: Failed opening required ‘__DIR__/vendor/autoload.php’ (include_path=’.:/opt/alt/php52/usr/share/pear:/opt/alt/php52/usr/share/php’) in /home/***/public_html/***.ca/wordpress/wp-content/plugins/php-compatibility-checker/wpengine-phpcompat.php on line 15