Strange error on createInjector "Unable to method intercept"

I have some experience with guice and i just tried guice-persist. But now i get a very strange error in my very simple module. This is my module:

public class VotingModule extends AbstractModule {

    @Override
    protected void configure() {
        bind(VotingService.class).to(VotingServiceImpl.class);
    }

}

I created a factory (this is for using this api, there is no main) to get an instance of the service:

    public static VotingService getService(final String persistenceUnit) {
    // initialization of dependency injection
    Injector i = Guice.createInjector(new JpaPersistModule(persistenceUnit), new VotingModule());
    // Starts persistence stuff (jpa is ready now)
    i.getInstance(PersistService.class).start();
    return i.getInstance(VotingService.class);
}

The VotingService and its implementation encapsulate simple data-base interactions. For this "VotingServiceImpl" only injects an EntityManager and uses @Transactionl on some methods. So why i get

    1) Unable to method intercept: com.prodyna.nabucco.groupware.voting.core.service.impl.VotingServiceImpl
  at com.prodyna.nabucco.groupware.voting.core.service.impl.VotingModule.configure(VotingModule.java:10)

? The error is thrown on this simple test:

   @Test
    public void test(){
        VotingService vs = VotingServiceFactory.getService();
    }

Edit This error only occurs if bound implementation uses @Transactional. So something went wrong with aop stuff but how to fix it? Edit

Ok i found the problem after some hours of debugging: The problem was a private constructor in interface' implementation. For vanilla guice private constructors are fine (imho good practice - you can't use "new"). but AOP (Interceptors) doesn't work with private constructors.

I think there should be some hints in doc about that?!