Language feature not implemented: System

i tried looking for the same post but nothing helped i really dont know why this is happining. the same exact script works on another pc with the same unity version but not on my pc. heres the code

 private var tosubtract:int=0;
 
 function Start(){
 
     var timeDiffrence = System.DataTime.now - System.DataTime.Parse(PlayerPrefs.GetString("SystemTime"));
     var tosubtract = timeDiffrence.Hours * 4;
     Pet.health-=tosubtract;
 }
 
 function OnApplicationQuit(){
     PlayerPrefs.SetString("SystemTime", System.DataTime.now.ToString());
     PlayerPrefs.Save();
 }
 
 function OnApplicationPause(paused: boolean){
     if(paused){
         PlayerPrefs.SetString("SystemTime", System.DataTime.now.ToString());
     }
     else{
         var timeDiffrence = System.DataTime.now - System.DataTime.Parse(PlayerPrefs.GetString("SystemTime"));
         var tosubtract = timeDiffrence.Hours * 4;
         Pet.health-=tosubtract;
     }
 }