Does it still activate when INS is true and the player is in car1 ?
I think what the game is saying is that;
INS AND !(... in car1)
is on possability,
and the other ones are,
OR !(... car2)
OR OR !(... car3)
Its a long shot, but what happens when you put ( ) around the whole OR cars section, so it would be;
ins AND (!(aP in a1) OR !(aP in a2) OR !(aP in a3))