Server 2008 R2: AD ACcounts locks out

Dear All,

I have server 2008 r2 with AD and GPO. Recently I realized that some of the users after putting up passwords wrong multiple times. They are locked out. I checked under GPO but I cannot see any setting which will do this. But when I do net accounts on client computers

Lock out duration: 30 minutes

Lockout Observation WIndows: 30 minutes

I checked all the settings in all GPO but there is nothing enabled.

Can some one please advise me as how I need to figure this problem out.

Thanks