Atomic Systems

After having the 'blank Driver Property Pop-out problem' solved for me by emrhd01 I've just realised I still have a problem.

All the icons and fields are in the driver properties but the the train icon with its tick square is not highlighted like the other fields which means I cannot tick or untick the square. Anyone help me on this one please?
Regards Spladger

With a free play scenario, the player drivable box cannot be ticked, as all trains with a driver icon can be used.