EntityManager null when trying to migrate to JBoss 7.1.1
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I am currently trying to migrate my web application from JBoss 5.1 to JBoss 7.1.1. I inject the entity manager into my jsp file but the entity manager is always null.

persistence.xml:

    <?xml version="1.0" encoding="UTF-8"?>
    <persistence version="1.0" xmlns="http://java.sun.com/xml/ns/persistence" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/persistence http://java.sun.com/xml/ns/persistence/persistence_1_0.xsd">
    	<!-- SSIS2 Productive Database --> 
    	<persistence-unit name="SSIS2" transaction-type="JTA">
    		<provider>org.hibernate.ejb.HibernatePersistence</provider>
    		<jta-data-source>java:/SSIS2DSprod</jta-data-source>
    		<properties>
    			<property name="hibernate.hbm2ddl.auto" value="update" />
    			<property name="hibernate.show_sql" value="false"/>
    			<property name="hibernate.dialect" value="org.hibernate.dialect.Oracle10gDialect"/> 
    		</properties>
    	</persistence-unit>
    </persistence> 

Example of Entity Manager injection in a JSP file:

    <%!	@PersistenceContext(unitName = "SSIS2")
        public EntityManager em;
    
        @Resource
        UserTransaction utx;
    %>

The deployment itself contains no errors, so what is the problem with the Entity Manager here? It works without problems on JBoss 5.1.

Edit:
datasource in standalone.xml: (ip-address and SSID removed)

    <datasource jta="true" jndi-name="java:/SSIS2DSprod" pool-name="SSIS2DSprod" enabled="true" use-java-context="true" use-ccm="true">
                        <connection-url>jdbc:oracle:thin:@ip-address:1531:SSID</connection-url>
                        <driver>oracle</driver>
                        <transaction-isolation>TRANSACTION_READ_COMMITTED</transaction-isolation>
                        <pool>
                            <prefill>true</prefill>
                            <use-strict-min>false</use-strict-min>
                            <flush-strategy>FailingConnectionOnly</flush-strategy>
                        </pool>
                        <security>
                            <user-name>ssis2</user-name>
                            <password>ssis2</password>
                        </security>
                    </datasource>