it need to be enabled on the manager
in the manager you have client control and manager control
you need to give full control to client so that this option appears ( or true scan option under mixed control)
follow these steps.
open sepm
click on clients
on the right hand side click on policies
click on the + sign on location specific setting
click on server control
change it to client control
click on apply
click
okay you should be fine.
http://img269.imageshack.us/img269/3328/sep2.png