This probem happens on JDK1.4, but has been fixed on jdk1.5:

When a server fails to serialize a answer message, in case of JDK1.4, a client will get an UnknownException, its nested exception is:
        org.omg.CORBA.portable.UnknownException: vmcid: 0x0 minor code: 0 completed

but on 1.5, a client will get MarshalException: CORBA BAD_PARAM 1330446342 Maybe; nested exception is:
        java.io.NotSerializableException: org.omg.CORBA.BAD_PARAM: vmcid: OMG minor code: 6 completed

The trace info is attached.
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