private IEnumerable bla()
{
yield return 1;
}

private IEnumerable<ScheduleMethod> bla()
{
yield return 1;
//or: yield return ScheduleMethod.wait(1);
//or: yield return ScheduleMethod.waitForFrames(1);
//ALL these three calls are equivalent !
}

private IEnumerable bla()
{
yield return 1;
yield return Scheduler.PROC_MODE.PROC_EARLIEST;
yield return 1;
}

private IEnumerable<ScheduleMethod> bla()
{
yield return 1;
yield return ScheduleMethod.PROC_EARLIEST;
yield return 1;
}

After adding AW 2.21 get ERROR:

error CS0308: The non-generic type 'System.Collections.IEnumerable' cannot be used with type arguments


using:
private IEnumerable<ScheduleMethod> myMainMethod() //ERROR:
{

	//....
       //yield return 1;
       yield return ScheduleMethod.wait( 1 );

}

and:
        private IEnumerable<ScheduleMethod> SizeWindow() //ERROR:
        {
            /*wait until the form is being resized*/
            while (ResizingNow == false)
            {
                //yield return 1;
                yield return ScheduleMethod.wait( 1 );
            }
            /*change the resolution*/
            EngFun.video_window(null, new Vector((this.panel_acknexWindow.Width),
                                                  this.panel_acknexWindow.Height, 0), 0, null);
            IsChangingSize = false;   //reset flag
            //yield return 1;
            yield return ScheduleMethod.wait( 1 );
        }