Java EE (Java Enterprise Edition) General Discussion

I have a strange problem.

By invoking a finder -method of an Entity-Bean, I get a ConcurrentModificationException
from the server, while concurrently trying to access an internal List:

The used server is Sun Java System Application Server Platform Edition 8.0 (build b57-fcs)

javax.ejb.EJBException: nested exception is: java.util.ConcurrentModificationException
java.util.ConcurrentModificationException
at java.util.AbstractList$Itr.checkForComodification(AbstractList.java:448)
at java.util.AbstractList$Itr.next(AbstractList.java:419)
at com.sun.ejb.containers.EntityContainer.preFind(EntityContainer.java:767)
at com.sun.ejb.containers.EntityContainer._getContext(EntityContainer.java:504)
at com.sun.ejb.containers.BaseContainer.getContext(BaseContainer.java:993)
at com.sun.ejb.containers.BaseContainer.preInvoke(BaseContainer.java:716)
at com.sun.ejb.containers.EJBHomeInvocationHandler.invoke(EJBHomeInvocationHandler.java:162)
at $Proxy74.findByAppointmentID(Unknown Source)
at com.space2go.server.entitybeans.appointment_notification._APPOINTMENT_NOTIFICATIONHome_Stub.findByAppointmentID(Unknown Source)
at com.space2go.server.sessionbeans.appointment.AppointmentOperationImpl.getAppointmentNotificationEntityBeanByAppoint
mentId(AppointmentOperationImpl.java:732)
........