hi, I am getting issue when I run sql Query having inner join, here is what I am doing very simple

ISession session = NHibernateHelper.GetCurrentSession();
        string query = string.Format("select Documents.TypeId from Documents inner join DocumentTrackingItems on Documents.Id = DocumentTrackingItems.DocumentId  WHERE DocumentTrackingItems.ItemStepId = {0} order by Documents.TypeId asc", 13);
        System.Collections.ArrayList document = (System.Collections.ArrayList)session.CreateSQLQuery(query, "document", typeof(Document)).List();

I am getting this exception

Exception Details: System.IndexOutOfRangeException: Id

what's wrong in my query? --- thanks