Problem to invoke the wM service from Sun Portal

We are using webMethods 6.5. We expose the service to Sun portal (Input as Documentlist) but Sun portal is not able to invoke the service.

Please find the below error message for your reference.

Error Message:

28 Mar 2011 11:00:28,282 ERROR com.cw.wad.ejb.session.ServicesImpl - An unspecified error has occured whilst communicating with WebMethods.
com.cw.wad.ejb.exception.WebMethodsException: java.rmi.MarshalException: CORBA MARSHAL 1398079745 Maybe; nested exception is:
org.omg.CORBA.MARSHAL: vmcid: SUN minor code: 257 completed: Maybe
at com.cw.wad.ejb.delegate.WebMethodsDelegate.getStock(WebMethodsDelegate.java:308)
at com.cw.wad.ejb.session.ServicesImpl.getStock(ServicesImpl.java:429)

Please help me to resolve the issue ASAP.