During the upgrade, you receive:
Microsoft Windows 2000 has detected software that is not completely installed on your computer. Windows 2000 Setup cannot continue until you finish installing this software. To finish the installation process for this software quit Windows 2000 Setup. Log off of your computer and then log back on again. Restart Windows 2000 Setup.If you log off / log on, you still get the same message.
The solution is to use Regedt32 to remove any information at:
HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\RunOnceEx AND HKEY_LOCAL_MACHINE\Software\Microsoft\Windows\CurrentVersion\Runonce