Download the zip file again and look at the code for yourself. The only way to get the admin subroutine to run is by running memberlist.cgi with the ?action=admin suffix. Something must be wrong with your system.
Donate to UBBDev today to help aid in Operational, Server and Script Maintenance, and Development costs.
Please also see our parent organization VNC Web Services if you're in the need of a new UBB.threads Install or Upgrade, Site/Server Migrations, or Security and Coding Services.