gistfile1.txt

using System.Threading.Tasks;
using System.Threading;
using System;

class X {
  static void Main ()
	{
		var x = new X ();
		x.Run ();
		Thread.Sleep (6000);
	}

	Task<int> AnimateAsync (Action callback)
	{
		callback ();
		return null;
	}

	void SecondLevel (Action callback)
	{
		callback ();
	}
	
	async void Run ()
	{
		var ret = await AnimateAsync (() => {
			SecondLevel (() => {
				// This throws System.ArgumentException: Value does not fall within the expected range.
				Console.WriteLine (this);
				});
		});
	}
}