GameObject won't move after got child

Sorry for the basic question, I am quite new in unity. So I use the FPS Controller from Unity. That is also my parent game object. I have another game object which is a book with the script down below…

So the problem is that after I set the parent of the book. I cant move…
I don’t get an error or something.

using System.Collections;
using System.Collections.Generic;
using UnityEngine;
using UnityStandardAssets.Characters.FirstPerson;
using UnityEngine.UI;
public class bookCollider : MonoBehaviour {

	FirstPersonController playerController=null;
	public Text clicktext;
	private bool isInTrigger=false;

	GameObject gameControllerObject;

	void Start(){
		 gameControllerObject = GameObject.FindGameObjectWithTag ("FirstPersonController");

		if (gameControllerObject != null)
		{
			playerController = gameControllerObject.GetComponent <FirstPersonController>(); //here is the error
		}
		if (playerController == null)
		{
			Debug.Log ("Cannot find 'FirstPersonController' script");
		}
	}

	void Update(){
		if (isInTrigger) {
			if (Input.GetKeyDown (KeyCode.F)) {
				gameObject.SetActive (false);
				clicktext.text = "u picked that item up";
				Invoke ("setTextToDefault", 2f);

			}
			if (Input.GetKeyDown (KeyCode.I)) {
				this.transform.parent = gameControllerObject.transform; //after here I cant move backwars/forward/sideways
				clicktext.text = "added to int";
				Invoke ("setTextToDefault", 2f);

			}
		}

	}

	private void setTextToDefault(){
		clicktext.text = "";
	}
	void OnTriggerEnter(Collider other) {
	//	Destroy(gameObject);
	//	playerController.PlayJumpSound ();
		clicktext.text=" f:pick up item.I:add to inventar";
		isInTrigger = true;
		Debug.Log ("jojojo");
	}

	void OnTriggerExit(Collider other) {
		clicktext.text="";
		isInTrigger = false;
		Debug.Log ("lol mate u out");
	}
}

Most likely, the collider in the book is blocking the controller from moving. Try setting the colliders to triggers when the book is parented.