I have nothing solid but by the looks of it I'd say the error comes from a chopper downwash script.
The problem seems to be that the script is trying to take the height of an object (in this case your tank) but can't do it. It says the information is already in an array.
So you'd need to either change the '_this' to the name of your tank of get rid of the 'getpos', debending on what the situation is with the script.. but I suggest you try to substitute that line in the script with the following.
(getpos
tankname select 2) < 30 && speed
tankname < 120 && isengineon
tanknameor it might just be that you're executing the script with wrong parameters. Maybe the script needs you to pass the units name into it when executing it, but you are passing some coordinates. You should check the instructions for the script.
G'luck