Error message with “sp.dll”

When I bootup my win2000 Pro with all user except Administrator, I received a message saying “Cannot import C:\WINNT\sp.dll: Not all data was successfully written to the registry. Some keys are open by the system or other processes.” I checked, there is sp.dll in the destination! How can I fix it? If you could answer, is sp.dll one of the system files for WIN2000 Pro? Thanks!