java.io.NotSerializableException WAS 6.0

Hi all

i am creating EAR Comp. from WASD 5.1.1 and deploying in WAS 6.0.
here one of my Stateless Session Bean calling another Stateless Session Bean. while calling , i am getting this exception.

java.rmi.MarshalException: Exception occurred in server thread; nested exception is:
      java.io.NotSerializableException
      at com.ibm.rmi.util.ProxyUtil.copyObjects(ProxyUtil.java:289)
      at com.ibm.CORBA.iiop.UtilDelegateImpl.copyObjects(UtilDelegateImpl.java:764)
      at javax.rmi.CORBA.Util.copyObjects(Util.java:315)
      at com.dcons.iss.ejb._ISS_Stub.handleRequest(_ISS_Stub.java:325)
      at com.dcons.iss.ejb.CountryBean.postRequest(CountryBean.java:142)
      at com.dcons.iss.ejb.EJSRemoteStatelessCountryBean_92aaebd3.postRequest(EJSRemoteStatelessCountryBean_92aaebd3.java:35)
      at com.dcons.iss.ejb._CountryRemote_Stub.postRequest(_CountryRemote_Stub.java:257)
      at com.dcons.iss.ejb.BeanHandlerFacadeBean.delegateRequest(BeanHandlerFacadeBean.java:74)
      at com.dcons.iss.ejb.EJSRemoteStatelessBeanHandlerFacade_7b05eacf.delegateRequest(EJSRemoteStatelessBeanHandlerFacade_7b05eacf.java:35)
      at com.dcons.iss.ejb._BeanHandlerFacadeRemote_Stub.delegateRequest(_BeanHandlerFacadeRemote_Stub.java:263)
      at com.dcons.iss.BeanHandler.doPost(BeanHandler.java:97)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:763)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
      at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1282)
      at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:673)
      at com.ibm.ws.webcontainer.webapp.WebAppRequestDispatcher.forward(WebAppRequestDispatcher.java:265)
      at com.dcons.iss.Controller.doPost(Controller.java:109)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:763)
      at javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
      at com.ibm.ws.webcontainer.servlet.ServletWrapper.service(ServletWrapper.java:1282)
      at com.ibm.ws.webcontainer.servlet.ServletWrapper.handleRequest(ServletWrapper.java:673)
      at com.ibm.ws.webcontainer.servlet.CacheServletWrapper.handleRequest(CacheServletWrapper.java:80)
      at com.ibm.ws.webcontainer.WebContainer.handleRequest(WebContainer.java:1802)
      at com.ibm.ws.webcontainer.channel.WCChannelLink.ready(WCChannelLink.java:84)
      at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleDiscrimination(HttpInboundLink.java:469)
      at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.handleNewInformation(HttpInboundLink.java:408)
      at com.ibm.ws.http.channel.inbound.impl.HttpInboundLink.ready(HttpInboundLink.java:286)
      at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.sendToDiscriminaters(NewConnectionInitialReadCallback.java:201)
      at com.ibm.ws.tcp.channel.impl.NewConnectionInitialReadCallback.complete(NewConnectionInitialReadCallback.java:103)
      at com.ibm.ws.tcp.channel.impl.WorkQueueManager.requestComplete(WorkQueueManager.java:566)
      at com.ibm.ws.tcp.channel.impl.WorkQueueManager.attemptIO(WorkQueueManager.java(Compiled Code))
      at com.ibm.ws.tcp.channel.impl.WorkQueueManager.workerRun(WorkQueueManager.java:952)
      at com.ibm.ws.tcp.channel.impl.WorkQueueManager$Worker.run(WorkQueueManager.java:1039)
      at com.ibm.ws.util.ThreadPool$Worker.run(ThreadPool.java(Compiled Code))
Caused by: java.io.NotSerializableException