SAP PI Sales Force Integration problem

Hello Experts,

   I am trying to integrate the response field from ECC--> PI ----> SalesForce server. The web service from salesforce is consumed by the SAP PI and we are trying to send the response structure to SalesForce by consuming its wsdl. The transaction is sucessfull in PI as in Moni it is showing processing sucessful. But when I am checking at the interface level through the RWB, it is giving me the following error.

" Message processing failed. Cause: com.sap.engine.interfaces.messaging.api.exception.MessagingException: SOAP: response message contains an error XIAdapter/PARSING/ADAPTER.SOAP_EXCEPTION - soap fault: INVALID_SESSION_ID: Invalid Session ID found in SessionHeader: Illegal Session"

I have checked the various threads in this forum , but i am unable to get the pinpointed answer for this error. Also I have gone thriugh the document given on the link..

http://www.sdn.sap.com/irj/scn/go/portal/prtroot/docs/library/uuid/50a76cfa-4966-2d10-aba7-da496d9b5bcf?QuickLink=index&…

But the step given in this are assuming that certain steps are done, I am not able to comprehend those.

Can some experts who have come across such error while inserting the payload in SalesForce software , pin pointedly guide me on this issue.

Thanks

Regards

Suk4023