EJB java.lang.ClassCastException

I'm using Eclipse with Glassfish for my first steps in Java EE. I've created three eclipse projects (JPA project, EJB project Web project). I've created a local EJB bean TestBean with a local interface TestBeanLocal:

@Stateless
@LocalBean
class TestBean implements TestBeanLocal {
  @Override
  public void doSomething(List<JPAEntity> myEntities) {
    for(JPAEntity a : myEntities) {

    }
  }
}

and a ManagedBean that uses the EJB:

@MangagedBean
public class MyBean {
    @EJB
    private TestBeanLocal testBean;

    @PostConstruct
    private void init() {
       //load JPAEntity from Database
       List<JPAEntity> myEntities = ....
       testBean.doSomething(myEntities);
    }
}

My problem is that I get a ClassCastException at the for loop in the TestBean.

java.lang.ClassCastException: us.mypackage.jpa.JPAEntity cannot be cast to us.mypackage.jpa.JPAEntity

I found another stackoverflow question that says that this error message is because of two different classloaders. How can I fix this? Can I tell EJB to use the same classloader that my webproject uses?