Duplicate objects does not work until last instance starts

i have made a turret and a player…
whenever the player is near to the turret, it starts to shoot at the player… this works fine.
So i created duplicate objects from the turret and placed in several places.
but those turrets does not start shooting when the player is near… but the last instance of the turret works fine… and after that turret starts to work, other turrets also work fine when the player is near them.
so the problem is, in order to get start the turrets, player has to go to the last instance of the turret…
can any one help me please…

Nice description of the problem. But without to know your logic we can’t really help.

Do you have a demo .blend?