[SOLVED] Stop counting score code error!

Hello! I am working at my video game, a simple 2D game, a kind of side scroller. Bellow you have some pics with game. The problem is with a code. I try to make a code that will stop the counting of score when the character hits an obstacle. I have used a collide function but from 3 days it gives me two errors. Bellow I give you the code and some pics with errors. I really need help and i will appreciate your help. Thanks!

The game

The code with funtion. Funtion is last.

 using UnityEngine;
 using System.Collections;
 
 public class CharacterMovment : MonoBehaviour {
     public float speed = 3.5f;
     public UIManager ui;
     
     
 
     // Use this for initialization
     void Start () {
 
         //ui = GetComponent<UIManager> ();    
 
     }
     
     // Update is called once per frame
     void Update () {
         /*if (Input.GetKey (KeyCode.D))
             transform.position += new Vector3 (speed * Time.deltaTime, 0.0f, 0.0f);
         if (Input.GetKey (KeyCode.A))
             transform.position -= new Vector3 (speed * Time.deltaTime, 0.0f, 0.0f);*/
         if (Input.GetKey (KeyCode.W))
             transform.position += new Vector3 (0.0f, speed * Time.deltaTime, 0.0f);
         if (Input.GetKey (KeyCode.S))
             transform.position -= new Vector3 (0.0f, speed * Time.deltaTime, 0.0f);
 
 
     }

     void OnCollisionEnter(Collision col)
     {
 
         if (col.GameObject.tag == "Obstacle")
         { ui.GameOverActivated; }
 
     }
     
 }
 

The erros

And this is UIManager. I dont konw, but maybe it will help you.

 using UnityEngine;
 using System.Collections;
 using UnityEngine.UI;
 
 
 public class UIManager : MonoBehaviour {
 
     public Text ScoreText;
     int score;
     bool GameOver;
 
     // Use this for initialization
     void Start () {
 
         score = 0;
         InvokeRepeating("ScoreUpdate", 0.3f, 0.01f);
         GameOver = false;
     
     }
     
     // Update is called once per frame
     void Update () {
 
         ScoreText.text = "SCORE  " + score;
     
     }
 
     void ScoreUpdate ()
     {
         if (GameOver == false)
         { score += 1; } 
     }
 
     public void GameOverActivated ()
     {
         GameOver = true;
     }
 
     public void Play ()
     {
 
         Application.LoadLevel("PrincipalLevel");
 
     }
 
     public void Pause ()
     {
 

That is it! I have search on google the problems, but i did not find something clear that cand help me. If is someone who can help me, I will appreciate. Thanks again!