Web Service Authentication problem

Hi

I have created a portal service and exposed this service as a webservice. I am consuming this webservice in webdynpro. Portal service contains 2 simple methods putdata() and getdatat().

When i access the webservice i am getting the following error.

"javax.xml.rpc.soap.SOAPFaultException: The User Authentification is not correct to access to the Portal Service com.sap.portal.prt.soap.GlobalData or the service was not found"

My Enterprise portal server is configured for SSO to back end R/3 system. I have checked for portal service availability and it is fine.

My Webdynpro and Portal are running on different machines. EP is running on AIX with SP11.

Any help please

Regards

NagaKishore V