Error:Class is included in a persistence unit,but is not mapped

Bonsoir,
je développe en J2ee ,je travail sur une application disktop de type JPA ,j'obtiens l'erreur suivant : Class is included in a persistence unit,but is not mapped
Voici mon fichier persistence.xml :

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="1.0" xmlns="http://www.oracle.com/webfolder/technetwork/jsc/xml/ns/persistence/index.html" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.oracle.com/webfolder/technetwork/jsc/xml/ns/persistence/index.html http://www.oracle.com/webfolder/technetwork/jsc/xml/ns/persistence/persistence_1_0.xsd">
<persistence-unit name="Portabilite">

<provider>oracle.toplink.essentials.PersistenceProvider</provider>
<class>com.portabilite.metier.Utilisateur</class>
<class>com.portabilite.metier.Service</class>
<class>com.portabilite.metier.Operateur</class>
<class>com.portabilite.metier.Local</class>
<class>com.portabilite.metier.Internationale</class>
<class>com.portabilite.metier.Facture</class>
<class>com.portabilite.metier.Demande</class>
<class>com.portabilite.metier.Data</class>

<!-- Les classes persistance -->

<!-- source de donnee -->

<properties>
<property name="toplink.jdbc.driver" value="com.mysql.jdbc.Driver"/>
<property name="toplink.jdbc.url" value="jdbc:mysql://localhost:3306/projetbd"/>
<property name="toplink.jdbc.user" value="root"/>
<property name="toplink.jdbc.password" value=""/>

<property name="toplink.target-database" value="MySQL4"/>

<!-- strategie face a une BD -->

<!-- <property name="toplink.ddl-generation" value="drop-and-create-tables"/> -->
<property name="toplink.ddl-generation.output-mode" value="database"/>
<property name="toplink.logging.level" value="FINE"/>

</properties>
</persistence-unit>

</persistence>



merci pour votre aide