If you're getting error 403 - Forbidden running your PHP script, the chances are that it's not owned by you or not executable.
From the terminal
>chown user.user scriptname.php
and/or
>chmod +x scriptname.php
You may also be able to change the ownership or read/write/execute permissions in your FTP program.
If you're unable to change either, please raise a support ticket an include details of which file to be changed.