In a later version of the script I initialised all the lists for decoys, pistons, gyros and the rotor locks to be able to get their count even if they are empty but I think you have removed them anyways.

List<IMyTerminalBlock> grid_block = new List<IMyTerminalBlock>(),
RotorLocks = new List<IMyTerminalBlock>(), AllPistons = new List<IMyTerminalBlock>(),
Decoys = new List<IMyTerminalBlock>(), Gyros = new List<IMyTerminalBlock>();

Oh, you deleted the decoy system from the script, not the ship.
Yes, that happened to me when the radar beacons were off after compiling the script. There is a block in the else-path which seems to be not initialised then. Try to run the script with beacons on after recompiling.
Also check the ownership of the radar beacon, sensors and PB (and timers you use them to trigger it). If you want to find enemies then they all have to have ownership "Me".
And methods of the radar displays are called when the displays are not there/found. If you don't use them, comment them out or remove them completely from the script.

thats great, but i'm try to adapt your script to a ship that i have built, and it keeps telling me that i'm missing stuff and it wont run

Easiest way: detach the two-ended motor and remove the decoy arms with ctrl-x. Then you can add a block or a few blocks in the gap and remove the remaining part of the two-ended motor.

what do i delete to get rid of the decoy system, i'm trying to use this for an eplorer ship, and my ship doesn't have a decoy deployment system and i don't want one

The Mk Id has a primitive output to the (right) textpanel and the MK Ie has the labelled target output with all contacts on the left front panel (BA [radar] Display left).
Just open the public text of these textpanels and close it again. Then go to the GPS and activate the waypoints you want. Currently I don't know any other way to get the target coordinates into the GPS.
If you want to try Darth Biomechs camera then just replace the turret on the MK Ie with it and rename it to "BA Turret". Then recompile the BA Control PB block. But basically the functionality is the same as any other turret. He just changed the ammo to do no damage and the RoF to be as low as possible afaik. E.g. you can't zoom and you just can look through it when controlling it but then it'll fight against the turret control of the PB.

which one just has the GPS dump to text panel, cuz i don't need the turret control. the turret control just seems rather useless if it's not bound to darth biomech's cam turret

Remark concerning GPS: Before you delete a waypoint, remove it from the HUD. Otherwise it may stay in the world.

Please tell me if something is not working. I didn't play survival or multiplayer yet.

As for [1.068] the small ship decoys have been fixed enabling you to take full ownership of the craft and to approach the target at higher speeds.