HNibernate报错了 XML validation error: 未声明“urn:nhibernate-mapping-2.2:nhibernate”元素。 .

请大神帮忙解决这个问题，这个HNibernate刚学，谢谢先。

出现这个错误：ConsoleApplication2.Mapping.User.hbm.xml(2,2): XML validation error: 未声明“urn:nhibernate-mapping-2.2:nhibernate”元素。

//这里是控制台

class Program

{
static void Main(string[] args)
{
Test();
}
static void Test()
{
NHibernateHelper db = new NHibernateHelper();
ISession session= db.GetSession();
using (var trans = session.BeginTransaction())
{
User user = new User();
user.Age = 123;
user.Name = "janekim";
session.Save(user);
trans.Commit();
}
}

//NHibernateHelper帮助类

namespace ConsoleApplication2

{
public class NHibernateHelper
{
private ISessionFactory sessfFactory;
public NHibernateHelper()
{
sessfFactory = GetSessionFactory();
}
private ISessionFactory GetSessionFactory()
{
Configuration config = new Configuration().AddAssembly(Assembly.GetExecutingAssembly());
return config.BuildSessionFactory();
}
public ISession GetSession()
{
return sessfFactory.OpenSession();
}
}
}

//这里是User.hbm.xml

<?xml version="1.0" encoding="utf-8" ?>

<nhibernate xmlns="urn:nhibernate-mapping-2.2">
<class name="ConsoleApplication2.Domain.User,ConsoleApplication2" table="User"></class>
<id name="Id" length="4">
<generator class="vative"></generator>
</id>
<property name="Name">
<column name="Name" sqltype="nvarchar" length="50" not-null="true"></column>
</property>
<property name="Age">
<column name="Age" sqltype="int" length="4" not-null="true"></column>
</property>
</nhibernate>

//App.config配置文件

<?xml version="1.0" encoding="utf-8" ?>
<nhibernate xmlns="urn:nhibernate-mapping-2.2">

  <class name="ConsoleApplication2.Domain.User,ConsoleApplication2" table="User"></class>
  
  <id name="Id" length="4">
    <generator class="vative"></generator>
  </id>
  
  <property name="Name">
    <column name="Name" sqltype="nvarchar" length="50" not-null="true"></column>
  </property>
  
  <property name="Age">
    <column name="Age" sqltype="int" length="4" not-null="true"></column>
  </property>

</nhibernate>