Php script problem

I recently installed this referrals script:

https://www.plebian.com/news.php?artc=4&s=6a1ee499fd2f2daafa740503b4c8e138

It works fine and all but the problem is it cannot execute its go.php command in a sub page. If you click on a referrals link on the index.php it will call the go.php file and go to mysite.com/go.phpREF# but if the visitor is in a sub page link mysite.com/contact it will go to mysite.com/contact/go.phpREF# but since it cannot find the go.php file in that directory it redirects to my main page insted of going to the referrals link . Can anybody help me? Thank You

Matthew