On XP pro SP3, Pybot 2 beta.

As I only want to use Spybor as an on demand scanner, I have set all its services to manual and none are started. However, when I do a manual check for updates I got an error event in Windows event viewer when trying manual update, saying:
Event Type: Error
Event Source: Service Control Manager
Event Category: None
Event ID: 7001
Date: 14/06/2011
Time: 21:48:57
User: N/A
Computer: DJDRRM3J
Description:
The Spybot-S&D 2 Updating Service service depends on the Secondary Logon service which failed to start because of the following error:
The service cannot be started, either because it is disabled or because it has no enabled devices associated with it.

I then checked dependencies of the Sybot Updating service and it appears that it requires secondarey log on service to be started (or at least enabled).

I have always set the secondary logon service to disabled.

Why does Spybot S&D update service require secondary log on service?

No other software update that I have requires it.