SBS 2011 - Event ID 24 on a certificate that has been Revoked in daily reports

I had this question after viewing SBS2011 - Expired Certificates - MSExchange Web Services Event ID 24.

My issue is that I get this error message in my daily reports:

MSExchange Web Services      24      08/03/2017 14:48:27      42
Event Details:    
The Exchange certificate [Subject] CN=Graham Sivill, OU=SBSUsers, OU=Users, OU=MyBusiness, DC=direct-ifc, DC=local [Issuer] CN=direct-ifc-DIRECTSERVER-CA [Serial Number] 23ABEFA6000100000012 [Not Before] 23/06/2014 11:23:58 [Not After] 23/06/2015 11:23:58 [Thumbprint] 00BC42E5C2B89AF7905F4F1DD69832DFD60B2EBE expired on 23/06/2015 11:23:58.

So reading up the fix for this error I ran this EMS command:
Remove-ExchangeCertificate -Server DirectServer -Thumbprint 00BC42E5C2B89AF7905F4F1DD69832DFD60B2EBE

This gets the response:
Confirm
Are you sure you want to perform this action?
Remove certificate with thumbprint 00BC42E5C2B89AF7905F4F1DD69832DFD60B2EBE from the computer's certificate store?
[Y] Yes  [A] Yes to All  [N] No  [L] No to All  [?] Help (default is "Y"): y
The certificate with thumbprint 00BC42E5C2B89AF7905F4F1DD69832DFD60B2EBE was found but is not valid for use with Exchange Server (reason: PkixKpServerAuthNotFoundInEnhancedKeyUsage).
    + CategoryInfo          : NotSpecified: (:) [Remove-ExchangeCertificate], InvalidOperationException
    + FullyQualifiedErrorId : 7884D31B,Microsoft.Exchange.Management.SystemConfigurationTasks.RemoveExchangeCertificate

[PS] C:\Windows\system32>

The certificate is listed in my revoked certificates.  How can I stop this message coming up, is there a way to delete the certificate permanently from the revoked certificates in the Certification Authority? If I right-click the certificate in the Certification Authority the only Tasks are:

View Attributes/Extensions
Export Binary Data
Unrevoke Certificate.

All of which seem irrelevant?

Any help with this would be appreciated.

Siv