Getting java.lang.ClassCastException during replication -

<Warning> <rmi> <080003> <RuntimeException thrown by rmi
server:
weblogic.cluster.replication.ReplicationManager.create(Lweblogic.rjvm.JVMID;ILwe
blogic.cluster.replication.ROID;Lweblogic.cluster.replication.Replicatable;)
 java.lang.ClassCastException: java.util.Hashtable
java.lang.ClassCastException: java.util.Hashtable
        at
weblogic.common.internal.ChunkedObjectInputStream.readObject(ChunkedObjectInputS
tream.java:99)
        at
weblogic.rjvm.MsgAbbrevInputStream.readObject(MsgAbbrevInputStream.java:103)
        at weblogic.cluster.replication.ReplicationManager_WLSkel.invoke(Unknown
Source)
        at weblogic.rmi.internal.BasicServerRef.invoke(BasicServerRef.java:455)
        at weblogic.rmi.internal.BasicServerRef$1.run(BasicServerRef.java:396)
        at
weblogic.security.service.SecurityServiceManager.runAs(SecurityServiceManager.ja
va:726)
        at
weblogic.rmi.internal.BasicServerRef.handleRequest(BasicServerRef.java:391)
        at
weblogic.rmi.internal.BasicExecuteRequest.execute(BasicExecuteRequest.java:30)
        at weblogic.kernel.ExecuteThread.execute(ExecuteThread.java:251)
        at weblogic.kernel.ExecuteThread.run(ExecuteThread.java:219)