I also found that to be true. The script needs "Register Globals On" To get around this problem you need to set up a localized php.ini file. This file is usually located in the directory that you have the issue with. Depending on the type of control you have with your server, you or your hosting provider can do this.
The reason for register globals off as a standard is due to issues with security. Register globals on allows for malicious people with some knowledge to hack the server or the site.
I am not proficient in php otherwise I could tell you what it would take to retify this issue in the script. But as one who knows the importance of this work and this script being available to install in as many server enviroments as possible, I would suggest we figure out how to financilly compensate David for the good work and help him afford to re-work his script or hire someone to help him re-work the script.