'Time' does not contain a definition for 'timeScale'

I have not had problems with this script in the past.. and all of a sudden it has started doing this: 'Time' does not contain a definition for 'timeScale'

using UnityEngine; using System.Collections;

public class PauseScript : MonoBehaviour {

 public GameObject transGray;
 public GameObject playButton;
 public bool paused;

 void Start () 
 {
     paused = false;    
     playButton.SetActive(false);
     transGray.GetComponent<Renderer>().enabled = false;

 }

 void Update () 
 {

 }

 public void Pause()
 {
     paused = !paused;

     if (paused) 
     {
         Time.timeScale = 0f;
         playButton.SetActive(true);
         transGray.GetComponent<Renderer>().enabled = true;
     } 
     else if (!paused) 
     {
         Time.timeScale = 1f;
         playButton.SetActive(false);;
         transGray.GetComponent<Renderer>().enabled = false;
     }
 }

}