ClassCastException on JMS Service startup

[Affan]

I am using Sun's JMS implementation from Dynamo app server. Whenever I
start my server with Unacked objects already in the Queue I get a
ClassCastException. This is strange because this even happens when I
haven't changed any classes, just a stop/start of the server. I
thought this was because of version differences between compiled class
versions and I added serial version Ids in all classes but didnt help.
Maybe its because of different classloaders etc.?

I am storing simple Java objects in the MessageObjects (no XML, etc.)

Here is the stackTrace:

**** info /atg/dynamo/service/j2ee/JMSService INFO Bound destination
messageQueue
into JNDI Namespace
**** info /atg/dynamo/service/j2ee/JMSService INFO Bound destination
emailQueue in
to JNDI Namespace
**** info /atg/dynamo/service/j2ee/JMSService INFO Bound destination
errorQueue in
to JNDI Namespace
**** Warning /atg/dynamo/service/j2ee/JMSService WARN Exception
**** Warning /atg/dynamo/service/j2ee/JMSService Message: null
**** Warning /atg/dynamo/service/j2ee/JMSService
java.lang.ClassCastException
**** Warning /atg/dynamo/service/j2ee/JMSService at
com.sun.jms.MessageImpl.deserializeMessageImpl(MessageImpl.java:2025)
**** Warning /atg/dynamo/service/j2ee/JMSService at
com.sun.jms.service.QueueSubscription.loadUnackedMessages(QueueSubscription.java:183)
**** Warning /atg/dynamo/service/j2ee/JMSService at
com.sun.jms.service.QueueImpl.loadLoggedMessages(QueueImpl.java:285)
**** Warning /atg/dynamo/service/j2ee/JMSService at
com.sun.jms.service.QueueImpl.<init>(QueueImpl.java:103)
**** Warning at com.sun.jms.service.ServiceRecoveryManager.createDestinationFromDBRow(ServiceRecoveryManager.java:162)
**** Warning at com.sun.jms.service.ServiceRecoveryManager.recoverDestinations(ServiceRecoveryManager.java:108)
**** Warning at com.sun.jms.service.ServiceRecoveryManager.recover(ServiceRecoveryManager.java:70)
**** Warning at com.sun.jms.service.JMSServiceImpl.initializationCheck(JMSServiceImpl.java:2148)
**** Warning at com.sun.jms.service.JMSServiceImpl.<init>(JMSServiceImpl.java:169)
**** Warning at com.sun.jms.service.JMSServiceImpl.getInstance(JMSServiceImpl.java:366)
**** Warning at com.sun.jms.service.JMSManagerImpl.startJMSService(JMSManagerImpl.java:85)
**** Warning at atg.j2ee.jms.JMSManagerService.doStartService(JMSManagerService.java:264)
**** Warning at atg.nucleus.GenericService.
startService(GenericService.java:484)

Any hints?

Thanks -

Affan