Digital signature verification error in SOAP sender channel

Hi,

We are having a SOAP to proxy scenario. We have exposed PI webservice to third party vendor. The vendor sends the message with a signature attached. We have loaded their certificates in keystore using which they sign the message. However, we see this error in sender SOAP channel everytime we receive a request.

com.sap.aii.security.lib.exception.SecurityException: SecurityException in method: verify( Message, byte[], CPALookupObject ). Message: SecurityException in method: verify( Message, byte[], CPALookupObject ). WSSEThread-Exception: SecurityException in method: run(). Message: [com.sap.ASJ.wssec.030197] Error while valdiating the digital signature. The error was com.sap.security.core.ws.wss.NoSecurityHeaderException No wsse:Security header has been defined for role soap:finalActor. Please verify the policy configuration... To-String: com.sap.security.core.policy.exceptions.VerifyException: [com.sap.ASJ.wssec.030197] Error while valdiating the digital signature. The error was com.sap.security.core.ws.wss.NoSecurityHeaderException No wsse:Security header has been defined for role soap:finalActor. Please verify the policy configuration..; To-String

I tried removing the Verification option in ICO for Requests but it gives out the same error. I found very little information for this on SCN. Any pointers would be really appreaciated.

Thanks,

Ravi