ok i have fixed them myself. for the tank entering the player, i used distance constraint actuator so that the tank keeps some distance from the player

and for the fps stuff i just deleted the scene and recreated it i guess it was a problem with the objects or may be because i made some of the objects to send message across to other objects

apart from all those i improved the accuracy of the enemy tanks using steering actuator(pathfinding). also if any body can help with the enemy bunkers; how do i make them to face the player and shoot the player while on the same spot (i guess you know how a bunker or rocket lunchers behave) the enemy bunker just seem to rotate every direction and not face the player. any help would be appreciated

i would upload the blend file in blendswap any time soon
