<?xml version="1.0"?>
<!DOCTYPE hibernate-mapping PUBLIC "-//Hibernate/Hibernate Mapping DTD 3.0//EN"
"http://hibernate.sourceforge.net/hibernate-mapping-3.0.dtd">
<hibernate-mapping>
    <class name="teste.Teste" table="teste">
        <id name="id" column="codigo">
            <generator class="increment" />
        </id>
        <property name="campo" type="string">
            <column name="campo" />
        </property>
    </class>
</hibernate-mapping>

Teste teste = new Teste();
teste.setCampo("campo");
session.save(teste);

17:08:10,687 INFO  [STDOUT] Hibernate: select max(codigo) from teste
17:08:10,734 ERROR [BasicPropertyAccessor] IllegalArgumentException in class: teste.Teste, setter method of property: id
17:08:10,734 ERROR [BasicPropertyAccessor] expected type: java.lang.Long, actual value: java.lang.Long
17:08:10,734 INFO  [STDOUT] org.hibernate.PropertyAccessException: IllegalArgumentException occurred while calling setter of teste.Teste.id
        at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPro
pertyAccessor.java:104)
        at org.hibernate.tuple.AbstractEntityTuplizer.setIdentifier(AbstractEnti
tyTuplizer.java:204)
        at org.hibernate.persister.entity.AbstractEntityPersister.setIdentifier(
AbstractEntityPersister.java:3261)
        at org.hibernate.event.def.AbstractSaveEventListener.performSave(Abstrac
tSaveEventListener.java:157)
        at org.hibernate.event.def.AbstractSaveEventListener.saveWithGeneratedId
(AbstractSaveEventListener.java:114)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.saveWithGene
ratedOrRequestedId(DefaultSaveOrUpdateEventListener.java:186)
        at org.hibernate.event.def.DefaultSaveEventListener.saveWithGeneratedOrR
equestedId(DefaultSaveEventListener.java:33)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.entityIsTran
sient(DefaultSaveOrUpdateEventListener.java:175)
        at org.hibernate.event.def.DefaultSaveEventListener.performSaveOrUpdate(
DefaultSaveEventListener.java:27)
        at org.hibernate.event.def.DefaultSaveOrUpdateEventListener.onSaveOrUpda
te(DefaultSaveOrUpdateEventListener.java:70)
        at org.hibernate.impl.SessionImpl.fireSave(SessionImpl.java:524)
        at org.hibernate.impl.SessionImpl.save(SessionImpl.java:514)
        at org.hibernate.impl.SessionImpl.save(SessionImpl.java:510)
        at servlet.ServletTeste.doGet(ServletTeste.java:24)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:697)
        at javax.servlet.http.HttpServlet.service(HttpServlet.java:810)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl
icationFilterChain.java:252)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF
ilterChain.java:173)
        at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFi
lter.java:81)
        at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(Appl
icationFilterChain.java:202)
        at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationF
ilterChain.java:173)
        at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperV
alve.java:213)
        at org.apache.catalina.core.StandardContextValve.invoke(StandardContextV
alve.java:178)
        at org.jboss.web.tomcat.security.CustomPrincipalValve.invoke(CustomPrinc
ipalValve.java:39)
        at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(Securit
yAssociationValve.java:159)
        at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValv
e.java:59)
        at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.j
ava:126)
        at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.j
ava:105)
        at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineVal
ve.java:107)
        at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.jav
a:148)
        at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java
:856)
        at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.proce
ssConnection(Http11Protocol.java:744)
        at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpo
int.java:527)
        at org.apache.tomcat.util.net.MasterSlaveWorkerThread.run(MasterSlaveWor
kerThread.java:112)
        at java.lang.Thread.run(Thread.java:595)
Caused by: java.lang.IllegalArgumentException: object is not an instance of decl
aring class
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
        at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.
java:39)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAcces
sorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:585)
        at org.hibernate.property.BasicPropertyAccessor$BasicSetter.set(BasicPro
pertyAccessor.java:42)
        ... 34 more

package teste;

public class Teste {
   private Long id;
   private String campo;
   
   public String getCampo() {
      return campo;
   }
   public void setCampo(String campo) {
      this.campo = campo;
   }
   public Long getId() {
      return id;
   }
   public void setId(Long id) {
      this.id = id;
   }
}

java.lang.IllegalArgumentException: object is not an instance of declaring class
        at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)