Hello there,
Are you running it with permissions of an account that has the rights to edit your certificates?
This issue may occur if the domain user account does not have Manage CA permission.
If you do have the permission, there are something you could try:
1.Restart the service.
2.Verify AD Replication.
The below thread discusses the same issue and you can try out some troubleshooting steps from this and see if that helps you to sort the Issue.
https://social.technet.microsoft.com/Forums/windowsserver/en-US/514663b0-bab7-483d-8804-c5578f60d12f/ca-cluster-new-certificate-template-issue-error-access-denied?forum=winserversecurity
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