How do I fix the following error?

Here is my errorMissingMethodException: Method not found: 'UnityEngine.GUI.Label'. Boo.Lang.Runtime.DynamicDispatching.MethodDispatcherFactory.ProduceExtensionDispatcher () Boo.Lang.Runtime.DynamicDispatching.MethodDispatcherFactory.Create () Boo.Lang.Runtime.RuntimeServices.DoCreateMethodDispatcher (System.Object target, System.Type targetType, System.String name, System.Object[] args) Boo.Lang.Runtime.RuntimeServices.CreateMethodDispatcher (System.Object target, System.String name, System.Object[] args) Boo.Lang.Runtime.RuntimeServices+c_AnonStorey14.<>m_7 () Boo.Lang.Runtime.DynamicDispatching.DispatcherCache.Get (Boo.Lang.Runtime.DynamicDispatching.DispatcherKey key, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.GetDispatcher (System.Object target, System.String cacheKeyName, System.Type[] cacheKeyTypes, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.GetDispatcher (System.Object target, System.Object[] args, System.String cacheKeyName, Boo.Lang.Runtime.DynamicDispatching.DispatcherFactory factory) Boo.Lang.Runtime.RuntimeServices.Invoke (System.Object target, System.String name, System.Object[] args) UnityScript.Lang.UnityRuntimeServices.Invoke (System.Object target, System.String name, System.Object[] args, System.Type scriptBaseType) Time.OnGUI () (at Assets/MyScripts/Time.js:12)

Sorry it is so long... here is the code that it is saying. I have no Idea what is wrong...

 var FinalTime;
 var buttonheight : int = 200;
 var buttonwidth : int = 200;
 function Start () 
 {
     FinalTime = Timer.finalTime;
 }
 
 function OnGUI () 
 {
     GUI.Box(Rect(1000, 400, buttonheight, buttonwidth), "Your Time");
     GUI.Label(Rect(100, 500, buttonheight, buttonwidth), "FinalTime");
 }