The subject behavior will occur if:
1. You install SP2 on a Windows 2000 computer on which IIS is NOT installed.
2. You install IIS.
3. You removed SP2.
4. You install SP3.
When you uninstalled SP2, the performance counter registry information was reset to the pre-SP2 state, removing required registry entries at:
Since SP3 setup knew that IIS was installed, it expected these keys.
To resolve this problem:
1. Uninstall IIS.
2. Re-install IIS.
NOTE: If you are going to remove a Service Pack, first uninstall any Windows components that you installed after the Service Pack, and re-install them after the Service Pack is removed.