What wrong with3.4?

I just delete 3.3 and install 3.4. Now I am having very strange errors:

function OnGUI() {
	if (GUI.Button(Rect(10,70,50,30),"Click"))
        Debug.Log("Clicked the button with text");
}

And I got below error when run:

MissingMethodException: Method not found: ‘GUI.Button’.
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__AnonStorey12.<>m__6 ()
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)

Besides, even I create a test project contain 1 test script just like above. When I click “Run” button, it is 2 times slower than in 3.3.

WHAT WRONG WITH THIS 3.4???

You probably have a script called GUI.js - don’t do that. No idea why it worked for you before.

Your other issue with slow transition to Play mode is unrelated (and, IIRC, reported elsewhere, not much we can do about it).