FULL PRODUCT VERSION :
java version "1.6.0-rc"
Java(TM) SE Runtime Environment (build 1.6.0-rc-b97)
Java HotSpot(TM) Client VM (build 1.6.0-rc-b97, mixed mode, sharing)

ADDITIONAL OS VERSION INFORMATION :
Microsoft Windows XP [Version 5.1.2600]

EXTRA RELEVANT SYSTEM CONFIGURATION :
JOnAS 4.7.6 (http://www.objectweb.org)

A DESCRIPTION OF THE PROBLEM :
JOnAS 4.7.6 is a 100% pure Java application (actually it is a Sun Microsoft certified J2EE 1.4 implementation written in Java, running ontop Sun JRE).

It is running well on JDK 4 and JDK 5, but JDK 6 makes it produce "ClassNotFoundException" with java.lang.String. This doesn't sound like a coding error because (a) the software is 100% pure Java, (b) the missing class is java.lang.String, (c) it runs well on JDK 4 and JDK 5.

REGRESSION. Last worked in version mustang

STEPS TO FOLLOW TO REPRODUCE THE PROBLEM :
Actually it is happening very sporadically, so I cannot tell you how to reproduce without running the EAR I have written inside of JOnAS 4.7.6 ontop of JDK 6.
Maybe it would be best if you contact the vendor of JOnAS 4.7.6 (it's an open source product): ###@###.###

EXPECTED VERSUS ACTUAL BEHAVIOR :
EXPECTED -
Should work as seen on JDK 4 and JDK 5.
ACTUAL -
Produces exceptions sometimes (always the same exception).

ERROR MESSAGES/STACK TRACES THAT OCCUR :
javax.jms.MessageFormatException: Error while deserializing the wrapped object: java.lang.ClassNotFoundException: [Ljava.lang.String;
        at org.objectweb.joram.client.jms.ObjectMessage.getObject(ObjectMessage.java:147)
        at de.quipsy.mdb.common.AbstractTrigger.onObjectMessage(Unknown Source)
        at de.quipsy.mdb.common.AbstractJmsObjectMessageDrivenBean.onMessage(Unknown Source)
        at sun.reflect.GeneratedMethodAccessor174.invoke(Unknown Source)
        at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
        at java.lang.reflect.Method.invoke(Method.java:597)
        at org.objectweb.jonas_ejb.container.JMessageEndpointProxy.invoke(JMessageEndpointProxy.java:214)
        at $Proxy0.onMessage(Unknown Source)
        at org.objectweb.joram.client.connector.InboundSession.onMessage(InboundSession.java:172)
        at org.objectweb.joram.client.jms.MessageConsumerListener.activateListener(MessageConsumerListener.java:449)
        at org.objectweb.joram.client.jms.MultiSessionConsumer.onMessage(MultiSessionConsumer.java:168)
        at org.objectweb.joram.client.jms.Session.onMessage(Session.java:1835)
        at org.objectweb.joram.client.jms.Session.run(Session.java:878)
        at org.objectweb.joram.client.jms.XASession.run(XASession.java:235)
        at org.objectweb.joram.client.connector.InboundSession.run(InboundSession.java:157)
        at org.objectweb.jonas_lib.JWorkManager.doMyWork(JWorkManager.java:386)
        at org.objectweb.jonas_lib.JWorkManager.nextWork(JWorkManager.java:443)
        at org.objectweb.jonas_lib.JWorkManager$WorkThread.run(JWorkManager.java:536)

REPRODUCIBILITY :
This bug can be reproduced often.

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Please contact ###@###.### to get insight of the open source of JOnAS 4.7.6.
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