instead of used this code
String mimeType = DataFlavor.javaJVMLocalObjectMimeType + ";class=" + CommandBeans.class.getName();
DataFlavor dataFlavor = new DataFlavor(mimeType, "command");
in my Transferable, TransferHandler class
i used
DataFlavor dataFlavor = new DataFlavor(CommandBeans.class,CommandBeans.class.getSimpleName());
that seem to have fixed the reference problem.