Need help with my code

Unity Engine
1

Hey i am making a script that are gonna spawn turrets on a plane in a tile system but i am having a problem actuly spawning the turret at a tile my problem is at GameObject newStructure = Instantiate(allStructures[structureIndex], lastHitObj.transform, Quaternion.identity); I can´t see the problem so would be nice with some help
and here is my whole script

using UnityEngine;
using System.Collections;

public class InGameGUI: MonoBehaviour {


//NGUI items
public bool  buildPanelOpen = false;
public TweenPosition buildPanelTweener;
public TweenRotation buildPanelArrowTweener;
//

//Placement Plane items
public Transform placementPlanesRoot;
public Material hoverMat;
public LayerMask placementLayerMask;
private Material originalMat;
private GameObject lastHitObj;
//

//build selection items
public Color onColor;
public Color offColor;
public GameObject[] allStructures;
public UISlicedSprite[] buildBtnGraphics;
private int structureIndex =0;
//

void  Start (){
	//reset the structure index, refresh the GUI
	structureIndex = 0;
	UpdateGUI();
}


void  Update (){
	if(buildPanelOpen) //if the build panel is open...
	{		
		//create a ray, and shoot it from the mouse position, forward into the game
		Ray ray= Camera.main.ScreenPointToRay (Input.mousePosition);
		RaycastHit hit;
		if(Physics.Raycast (ray, out hit, 1000f, placementLayerMask)) //if the RAY hits anything on right LAYER, within 1000 meters, save the hit item in variable "HIT", then...
		{
			if(lastHitObj) //if we had previously hit an object...
			{
				lastHitObj.renderer.material = originalMat; //visually de-select that object
			}
			
			lastHitObj = hit.collider.gameObject; //replace the "selected plane" with this new plane that the raycast just hit
			originalMat = lastHitObj.renderer.material; //store the new plane's starting material, so we can reset it later
			lastHitObj.renderer.material = hoverMat; //set the plane's material to the highlighted look
		}
		else //...if the raycast didn't hit anything (ie, the mouse moved outside the tiles) ...
		{
			if(lastHitObj) //if we had previously hit something...
			{
				lastHitObj.renderer.material = originalMat; //visually de-select that object
				lastHitObj = null; //nullify the plane selection- this is so that we can't accidentally drop turrets without a proper and valid location selected
			}
		}
		
		//drop turrets on click
		if(Input.GetMouseButtonDown(0)  lastHitObj) //left mouse was clicked, and we have a tile selected
		{
			if(lastHitObj.tag == "PlacementPlane_Open") //if the selected tile is "open"...
			{
				//drop the chosen structure exactly at the tile's position, and rotation of zero. See how the "index" comes in handy here? :)
	GameObject newStructure = Instantiate(allStructures[structureIndex], lastHitObj.transform, Quaternion.identity);
				//set the new structure to have a random rotation, just for looks
				newStructure.transform.localEulerAngles.y = (Random.Range(0,360));
				//set this tile's tag to "Taken", so we can't double-place structures
				lastHitObj.tag = "PlacementPlane_Taken";
			}
		}
	}	
}

//
//-- Custom Functions --//

//One Update to Rule them All!
//this function will eventually contain all generic update events
//this makes sure we don't have the same small parts being called over and over in different ways, throughout the script
void  UpdateGUI (){
	//Go through all structure buttons (the buttons in the build panel), and set them to "off"
	foreach(UISlicedSprite theBtnGraphic in buildBtnGraphics)
	{
		theBtnGraphic.color = offColor;
	}
	//set the selected build button to "on"
	buildBtnGraphics[structureIndex].color = onColor;
}

//Called whenever a structure choice is clicked (the button in the build panel)
void  SetBuildChoice ( GameObject btnObj  ){
	//when the buttons are clicked, they send along thier GameObject as a parameter, which is caught by "btnObj" above
	//we then use that btnObj variable, and get it's name, so we can easily check exactly which button was pressed
	string btnName = btnObj.name;
	
	//here, we set an "index"  based on which button was pressed
	//by doing this, we can easily tell, from anywhere in the script, which structure is currently selected
	//also, if we order things just right, we can use this "index" to reference the correct array items automatically!
	if(btnName == "Btn_Cannon")
	{
		structureIndex = 0;
	}
	else if(btnName == "Btn_Missile")
	{
		structureIndex = 1;
	}
	else if(btnName == "Btn_Mine")
	{
		structureIndex = 2;
	}
	
	//call this as a seperate function so that, as things get more complicated,
	//all GUI can be updated at once, in the same way
	UpdateGUI();
}

//Happens whenever the build panel arrow button is clicked
void  ToggleBuildPanel (){
	if(buildPanelOpen) //is the build panel already open? if so, do this...
	{
		//hide all build tiles
		foreach(Transform thePlane in placementPlanesRoot)
		{
			thePlane.gameObject.renderer.enabled = false;
		}
		
		//fly out the build panel
		buildPanelTweener.Play(false);
		//rotate the build panel arrow
		buildPanelArrowTweener.Play(false);
		//mark the panel as "closed"
		buildPanelOpen = false;
	}
	else //...the build panel was closed, so instead do this...
	{
		//show all build tiles
		foreach(Transform thePlane in placementPlanesRoot)
		{
			thePlane.gameObject.renderer.enabled = true;
		}
		
		//fly in the build panel
		buildPanelTweener.Play(true);
		//rotate the build panel arrow
		buildPanelArrowTweener.Play(true);
		//mark the panel as "open"
		buildPanelOpen = true;
	}	
}
}
2

Instantiate returns an object of type Object and not GameObject. That’s why you need a cast.

GameObject newStructure = (GameObject) Instantiate(allStructures[structureIndex], lastHitObj.transform, Quaternion.identity);
3

awesome thanks for the help gonna try it out