No of Useronline always return 0

 iam using asp.net 2.0 with msaccess as backend
but when i try this
Label1.Text = "usersonline=" & Membership.GetNumberOfUsersOnline

 or this
Label1.Text = "usersonline=" & Membership.GetNumberOfUsersOnline.ToString 
 
it alwasy return 0
 
why is that, do i need aspnetdb database as well, i also added that, but still it always returns 0 , any reasons
 
 
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