Thanks bob.kahlon for the heads up :D
When applying Windows 2000 Service Pack 3 (SP3) on a debug version of Windows 2000 that has been upgraded to Windows 2000 Service Pack 2 (SP2), you may receive an error message. This problem occurs because a registry key that is set during the installation of Windows 2000 SP2 conflicts with the Update.exe install program. Microsoft has released a script that you can run before you apply Windows 2000 SP3 that removes the registry key. Download now to prevent this error from occuring.