Hibernate version: 3.1.1
Hibernate Annotations version: 3.1beta8
Hibernate EntityManager version: 3.1beta6

Tomcat version: 5.5.15
PostgreSQL version: 8.1.2

In my class DbUtil (aka HibernateUtil) I have this static initializer:
static {
try {
emf = Persistence.createEntityManagerFactory("hska");
}
catch (Throwable e) {
log.fatal("Initial EntityManagerFactory cannot be created", e);
throw new ExceptionInInitializerError(e);
}
}

There is also WEB-INF/classes/META-INF/persistence.xml:
<?xml version="1.0" encoding="ISO-8859-1"?>

<persistence>
<persistence-unit name="hska" transaction-type="RESOURCE_LOCAL">
<provider>org.hibernate.ejb.HibernatePersistence</provider>
<non-jta-data-source>jdbc/hskadb</non-jta-data-source>

<!-- C l a s s e s -->
<class>de.hska.kundenverwaltung.db.KundeEntity</class>
...

<properties>
<!-- P o s t g r e S Q L -->
<property name="hibernate.dialect" value="org.hibernate.dialect.PostgreSQLDialect"/>
<property name="hibernate.connection.url" value="jdbc:postgresql:hskadb"/>
<property name="hibernate.connection.driver_class" value="org.postgresql.Driver"/>

<!-- G e n e r a l -->
<property name="hibernate.connection.isolation" value="2"/>
<property name="hibernate.connection.datasource" value="java:comp/env/jdbc/hskadb"/>
<property name="hibernate.connection.autocommit" value="false"/>
<property name="hibernate.show_sql" value="false"/>

<!-- C a c h i n g -->
<property name="hibernate.cache.provider_class" value="org.hibernate.cache.EhCacheProvider"/>
<property name="hibernate.cache.use_query_cache" value="true"/>
</properties>
</persistence-unit>
</persistence>

When I start Tomcat the class DbUtil (see above) is initialized and I get this stack trace:
FATAL packaging.PersistenceXmlLoader - hska RESOURCE_LOCAL
FATAL util.DbUtil - Initial EntityManagerFactory cannot be created
javax.persistence.PersistenceException: java.lang.NullPointerException
at org.hibernate.ejb.Ejb3Configuration.createEntityManagerFactory(Ejb3Configuration.java:173)
at org.hibernate.ejb.HibernatePersistence.createEntityManagerFactory(HibernatePersistence.java:103)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:37)
at javax.persistence.Persistence.createEntityManagerFactory(Persistence.java:27)
at de.hska.util.DbUtil.<clinit>(DbUtil.java:30)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:164)
at de.hska.util.HskaFilter.init(HskaFilter.java:29)
at org.apache.catalina.core.ApplicationFilterConfig.getFilter(ApplicationFilterConfig.java:223)
at org.apache.catalina.core.ApplicationFilterConfig.setFilterDef(ApplicationFilterConfig.java:304)
at org.apache.catalina.core.ApplicationFilterConfig.<init>(ApplicationFilterConfig.java:77)
at org.apache.catalina.core.StandardContext.filterStart(StandardContext.java:3598)
at org.apache.catalina.core.StandardContext.start(StandardContext.java:4168)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1012)
at org.apache.catalina.core.StandardHost.start(StandardHost.java:718)
at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1012)
at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:442)
at org.apache.catalina.core.StandardService.start(StandardService.java:450)
at org.apache.catalina.core.StandardServer.start(StandardServer.java:700)
at org.apache.catalina.startup.Catalina.start(Catalina.java:551)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:275)
at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
Caused by: java.lang.NullPointerException
at org.hibernate.ejb.packaging.PersistenceXmlLoader.deploy(PersistenceXmlLoader.java:68)
at org.hibernate.ejb.Ejb3Configuration.createEntityManagerFactory(Ejb3Configuration.java:139)
... 25 more
ERROR [localhost].[/hska] - Exception starting filter dbUtil

I believe this has been changed in CVS already (i experienced the same nullpointer bug). A workaround is the following:

Right, this was a stupid bug from my side. This is fixed in CVS