Error consuming web service

I am getting the following SOAP fault while consuming a client web service:

<?xml version="1.0" encoding="UTF-8"?>

<SOAP-ENV:Envelope xmlns:SOAP-ENV=“” xmlns:SOAP-ENC=“” xmlns:xsd=“” xmlns:xsi=“”>
<SOAP-ENV:Header xmlns:SOAP-ENV=“”></SOAP-ENV:Header>SOAP-ENV:BodySOAP-ENV:Fault
[ISS.0088.9251] JAX-RPC Handler failed to process the message
<webM:detailEntry xmlns:webM=“” xmlns:xml=“”>
<webM:message xml:lang=""> WS Security processing failed : Unable to resolve private key for signing or decrypting the message</webM:message>

I am using security policy Sign_Auth_for_consumer.xml. Our client provided us a certificate to validate the connection to their server and another certificate for the web service. I added both in the definition of the web service end point.
Even though I am getting that SOAP response I am not sure of is if I am hitting their web service or that message comes from our IS.
Any help is appreciated.
Thank you.

Check if the private key path mentioned in the endpoint is correct.