Even with UAC disabled, are you using an administrative command prompt?
The security token for administratively running IISRESET isn't there under a normal command prompt even if you've moved the UAC slider to "Never Notify".
You can follow these steps:
- Open PowerShell
- Type Regedit then hit enter
- Browse to HKEY_LOCAL_MACHINE\SOFTWARE\MicrosoftWindows\CurrentVersion\policies\system
- Double click on EnableLUA
- Change the Value data to a 0
- Click OK, then reboot the server
To completely disable UAC, and then try running IISRESET from a normal cmd prompt, but it isn't good practice to completely disable UAC on any server.