Many thanks! I obviously hadn't thought to change the permissions at the ISM level. Went in and changed who was running the script with anonymous access from IUSER to my account and everything worked great!
Like paulbort says, it is a security hazard to have the script running privileged commands for anybody.
My suggestion was to remove Anonymous access - this would require some other form of User authentication before the script was run - either "Integrated NT", or Cleartext. If you are on the Internet, I would recommend Cleartext over HTTPS.
"Experience is a wonderful thing. It enables you to recognize a mistake when you make it again."