类型或命名空间名称'；得分'；找不到

我不知道为什么，但我看到了这个错误。。我遵循了一个教程，到目前为止没有错过任何东西，但现在我已经学会了。

找不到类型或命名空间名称"Score"（是否缺少using指令或程序集引用？）

PlayerMotor.cs

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
public class PlayerMotor : MonoBehaviour
{
    private CharacterController controller;
    private Vector3 moveVector;
    private float speed = 10.0f;
    private float verticalVelocity = 0.0f;
    private float gravity = 12.0f;
    private float animationDuration = 3.0f;
    private bool isDead = false;
    void Start () {
        controller = GetComponent<CharacterController>();
    }
    void Update () {
        if (isDead)
            return;
        if(Time.time < animationDuration)
        {
            controller.Move(Vector3.forward * speed * Time.deltaTime);
            return;
        }
        moveVector = Vector3.zero;
        if(controller.isGrounded)
        {
            verticalVelocity = -0.5f;
        }
        else
        {
            verticalVelocity -= gravity * Time.deltaTime;
        }
        // X - Left and Right
        moveVector.x = Input.GetAxisRaw("Horizontal") * speed;
        // Y - Up and Dow
        moveVector.y = verticalVelocity;
        // Z - Forward and Backward
        moveVector.z = speed;

        controller.Move (moveVector * Time.deltaTime);
    }
    public void SetSpeed(float modifier)
    {
        speed = 10.0f + modifier;
    }
    private void OnControllerColliderHit (ControllerColliderHit hit)
        {
        if (hit.point.z > transform.position.z + controller.radius)
            Death();
        }
    private void Death()
    {
        isDead = true;
        GetComponent<Score>().OnDeath();
    }
}

Score.cs

using UnityEngine;
using System.Collections;
using UnityEngine.UI;
public class Score : MonoBehaviour
{
    private float score = 0.0f;
    private int difficultyLevel = 1;
    private int maxDifficultyLevel = 10;
    private int scoreToNextLevel = 10;
    private bool isDead = false;
    public Text scoreText;
    void Update () {
        if (isDead)
            return;
        if (score >= scoreToNextLevel)
            LevelUp();
        score += Time.deltaTime * difficultyLevel;
        scoreText.text = ((int)score).ToString ();
    }
    void LevelUp()
    {
        if (difficultyLevel == maxDifficultyLevel)
            return;
        scoreToNextLevel *= 2;
        difficultyLevel++;
        GetComponent<PlayerMotor>().SetSpeed (difficultyLevel);
        Debug.Log (difficultyLevel);
    }
    public void OnDeath()
    {
        isDead = true;
    }
}

GameObject.Find("Player").GetComponent<Score>().OnDeath();