Win xp, System lock event in event viewer

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C#2.0

C#

Hello,

I'm Working on C# application which reads event viewer security log entries from Win xp to track user Login/Logoff and Lock/unlock activities in that I found, default Win XP does not add entries for Lock/Unlock events. So I enabled to Local Security Policy-->Audit policies as suggested(Google search).

After enabling policies I found entries only for unlock event and not for lock event.

How do I track system lock event in Win xp?