Hibernate version:1.0.2

Mapping documents:
test (1)---------->subtest (N)
test.hbm.xml:
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="Entity.Test,Entity" table="Test" lazy="true">
<composite-id>
<key-property name="keyOne" column="keyOne" type="Int32" />
<key-property name="keyTwo" column="keyTwo" type="Int32" />
</composite-id>
<property name="myproperty" column="myproperty" type="String"/>
<property name="myint" column="myint" type="Int32"/>

<bag name="SubTestList" cascade="save-update" inverse="true" lazy="true">
<key>
<column name="keyOne"/>
<column name="keyTwo"/>
</key>
<one-to-many class="Entity.SubTest,Entity"/>
</bag>
</class>
</hibernate-mapping>

subtest.hbm.xml:
<hibernate-mapping xmlns="urn:nhibernate-mapping-2.0">
<class name="Entity.SubTest,Entity" table="SubTest" lazy="true">
<composite-id>
<key-property name="keyOne" column="keyOne" type="Int32" />
<key-property name="keyTwo" column="keyTwo" type="Int32" />
<key-property name="keyThree" column="keyThree" type="Int32" />
</composite-id>

<property name="mySubproperty" column="myproperty" type="String"/>

<many-to-one name="Parent" class="Entity.Test,Entity" insert="false" update="false">
<column name="keyOne"/>
<column name="keyTwo"/>
</many-to-one>
</class>
</hibernate-mapping>

Class: (ignore),
and already override Equals() and GetHashCode().

test code:
public void test()
{
// already add data:
//test(1,1"test",15)
//subtest(1,1,1,"sub1")
//subtest(1,1,2,"sub2")
SubTest sub = session.Get(typeof(SubTest), new SubTest(1, 1, 1)) as SubTest;

Assert.IsNotNull(sub .Parent);
Assert.IsTrue(sub .Parent.myint == 15);
}


run test throw exception:

test: NHibernate.HibernateException : Creating a proxy instance failed
----> System.MissingMethodException : Constructor on type 'CProxyTypeTestSystem_INHibernateProxy_ISerializable2' not found.

why? I don't know this exception,
please,help me,thank you