Nhibernate配置出了问题

执行程序时，提示以下错误：
{NHibernate.MappingException: Could not compile the mapping document: Entity.UserInfo.hbm.xml ---> System.Collections.Generic.KeyNotFoundException: 给定关键字不在字典中。  。。
好像是映射文件不能找到：Could not compile the mapping document: Entity.UserInfo.hbm.xml

ISessionFactory _sessionFactory;

            NHibernate.Cfg.Configuration cfg = new NHibernate.Cfg.Configuration();
            cfg.AddAssembly("Entity");

            _sessionFactory = cfg.BuildSessionFactory();

            using (NHibernate.ISession session = _sessionFactory.OpenSession())
            {
 
                try
                {
                    IQuery query = session.CreateQuery("select * from UserInfo ");
                    IList<UserInfo> list = query.List<UserInfo>();
                    if (list.Count > 0)
                    {
                        return list[0];
                    }

                    else
                        return null;
                }
                catch (System.Exception ex)
                {
                    throw ex;
                }
                finally
                {
                    session.Close();
                }
            }
这段代码出现错误。。 各位大侠帮忙解决一些喽。。 O(∩_∩)O谢谢~\(≧▽≦)/~啦啦啦！！