Не могу добавить скрипт в GameObject

Question

Я не могу добавить скрипт в свой GameObject. Я не знаю почему.

это выглядит как проблема, и не добавляет

using UnityEngine.;
using System.Collections;

public class zombieScript : MonoBehaviour
{
    //declare the transform of our goal (where the navmesh agent will move towards) and our navmesh agent (in this case our zombie)
    private Transform goal;
    private NavMeshAgent agent;

    // Use this for initialization
    void Start()
    {

        //create references
        goal = Camera.main.transform;
        agent = GetComponent<NavMeshAgent>();
        //set the navmesh agent's desination equal to the main camera's position (our first person character)
        agent.destination = goal.position;
        //start the walking animation
        GetComponent<Animation>().Play("walk");
    }


    //for this to work both need colliders, one must have rigid body, and the zombie must have is trigger checked.
    void OnTriggerEnter(Collider col)
    {
        //first disable the zombie's collider so multiple collisions cannot occur
        GetComponent<CapsuleCollider>().enabled = false;
        //destroy the bullet
        Destroy(col.gameObject);
        //stop the zombie from moving forward by setting its destination to it's current position
        agent.destination = gameObject.transform.position;
        //stop the walking animation and play the falling back animation
        GetComponent<Animation>().Stop();
        GetComponent<Animation>().Play("back_fall");
        //destroy this zombie in six seconds.
        Destroy(gameObject, 6);
        //instantiate a new zombie
        GameObject zombie = Instantiate(Resources.Load("zombie", typeof(GameObject))) as GameObject;

        //set the coordinates for a new vector 3
        float randomX = UnityEngine.Random.Range(-12f, 12f);
        float constantY = .01f;
        float randomZ = UnityEngine.Random.Range(-13f, 13f);
        //set the zombies position equal to these new coordinates
        zombie.transform.position = new Vector3(randomX, constantY, randomZ);

        //if the zombie gets positioned less than or equal to 3 scene units away from the camera we won't be able to shoot it
        //so keep repositioning the zombie until it is greater than 3 scene units away. 
        while (Vector3.Distance(zombie.transform.position, Camera.main.transform.position) <= 3)
        {

            randomX = UnityEngine.Random.Range(-12f, 12f);
            randomZ = UnityEngine.Random.Range(-13f, 13f);

            zombie.transform.position = new Vector3(randomX, constantY, randomZ);
        }

    }

}