X509 Certificate

I am trying to test web services using the WS-Tester and I get an error when I try to invoke. Found below is the error:

WSE910: An error happened during the processing for a response message, and you can find the error in the inner exception. You can also find the response message in the Response property.

Does anybody know what would be the reason for this error?

I am also getting an error when I select a x509 certificate, when I try to replace the "MfgPolicy" in WseConfigEditor. Found below is the error that I am getting:

"Selected Certificate does not support Digital Signature"

Please advise what can I do to fix this two errors. Thanks for your help in advance.

Dhaval Jariwala