JPA Error - ClassCastException: SerialContext cannot be cast to DataSource?

If you happen to get this ClassCastException error while developing with JPA 2.0 and/or EclipseLink:

[EL Severe]: 2010-02-16 04:02:45.519--ServerSession(26903574)--
java.lang.ClassCastException: com.sun.enterprise.naming.impl.SerialContext cannot be cast to javax.sql.DataSource
        at org.eclipse.persistence.sessions.JNDIConnector.connect(JNDIConnector.java:110)
        at org.eclipse.persistence.sessions.JNDIConnector.connect(JNDIConnector.java:94)
        at org.eclipse.persistence.sessions.DatasourceLogin.connectToDatasource(DatasourceLogin.java:162)
        at org.eclipse.persistence.internal.sessions.DatabaseSessionImpl.loginAndDetectDatasource(DatabaseSessionImpl.java:584)
        at org.eclipse.persistence.internal.jpa.EntityManagerFactoryProvider.login(EntityManagerFactoryProvider.java:228)
        at org.eclipse.persistence.internal.jpa.EntityManagerSetupImpl.deploy(EntityManagerSetupImpl.java:368)
        at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.getServerSession(EntityManagerFactoryImpl.java:151)
        at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManagerImpl(EntityManagerFactoryImpl.java:207)
        at org.eclipse.persistence.internal.jpa.EntityManagerFactoryImpl.createEntityManager(EntityManagerFactoryImpl.java:195)
        at user.UserTest.setUp(UserTest.java:39)
        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:597)
        at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:44)
        at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
        at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:41)
        at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:27)
        at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:73)
        at org.junit.runners.BlockJUnit4ClassRunner.runChild(BlockJUnit4ClassRunner.java:46)
        at org.junit.runners.ParentRunner.runChildren(ParentRunner.java:180)
        at org.junit.runners.ParentRunner.access$000(ParentRunner.java:41)
        at org.junit.runners.ParentRunner$1.evaluate(ParentRunner.java:173)
        at org.junit.internal.runners.statements.RunBefores.evaluate(RunBefores.java:28)
        at org.junit.internal.runners.statements.RunAfters.evaluate(RunAfters.java:31)
        at org.junit.runners.ParentRunner.run(ParentRunner.java:220)
        at junit.framework.JUnit4TestAdapter.run(JUnit4TestAdapter.java:39)
        at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.run(JUnitTestRunner.java:422)
        at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.launch(JUnitTestRunner.java:931)
        at org.apache.tools.ant.taskdefs.optional.junit.JUnitTestRunner.main(JUnitTestRunner.java:785)

I solved this problem by removing the non-jta-data-source in the persistence.xml below:

<?xml version="1.0" encoding="UTF-8"?>
<persistence version="2.0" 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_2_0.xsd">
  <persistence-unit name="PragmaticDciPU" transaction-type="RESOURCE_LOCAL">
    <provider>org.eclipse.persistence.jpa.PersistenceProvider</provider>
    <class>user.internal.UserMixin</class>
    <non-jta-data-source />
    <exclude-unlisted-classes>true</exclude-unlisted-classes>
    <properties>
      <property name="eclipselink.ddl-generation" value="create-tables"/>
      <property name="javax.persistence.jdbc.driver" value="org.apache.derby.jdbc.ClientDriver"/>
      <property name="javax.persistence.jdbc.url" value="jdbc:derby://localhost/pragmaticdci"/>
      <property name="javax.persistence.jdbc.user" value="app"/>
      <property name="javax.persistence.jdbc.password" value="app"/>
    </properties>
  </persistence-unit>
</persistence>