“无法实例化”NHibernate.QueryException由组合的Linq查询引发

执行下面的NHibernate.Linq语句将引发 "could not instantiate: Reservation001.Services.ReservationDto"

var inOneStep = (from r in session.Linq<Models.ReservationHeader>()
    select new ReservationDto(r.Current));
return inOneStep;

但是,在将上述内容拆分为两个查询后,如果对第一个查询的结果调用ToList(),则代码执行得很好。

var step1 = (from r in session.Linq<Models.ReservationHeader>()
     select r).ToList();
var step2 = from z in step1
     select new ReservationDto(z.Current);
return step2;

为什么单语句版本会引发异常?

本