Error Response for signature Validation failure

One thing I did not specify in the usage of XML DSIG for Registry,
is what happens if there is a signature validation failure .

Specifically, the behaviour needs to be specified for the case
where the Registry's validation of the Registry Client's signature
fails. In this case the Registry would have to return and ebXML error
message.

But should there be a more detailed error code ? In Version 1.0 of the
Registry Spec, the DTD at the end seems to be indicate that
an error code from ebMS (ebXML Message Service) specification would
be returned. 


-- 
Sekhar