Active Directory Certificate Services (AD CS) records critical configuration settings in the registry and may not start or function properly if this information becomes corrupted or is deleted.
Fix the SubjectTemplate registry key
By default, certification authority (CA) registry configuration information is located under HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\CA name.
If the event log message states that the SubjectTemplate registry key is not valid, then you can update the registry entry with correct information.
The location of this registry key is HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\CA name\SubjectTemplate.
A valid SubjectTemplate string can include:
To perform this procedure, you must have membership in local Administrators, or you must have been delegated the appropriate authority.
Caution: Incorrectly editing the registry might severely damage your system. Before making changes to the registry, you should back up any valued data.
To resolve registry-related problems:
On the computer hosting the CA, click Start, type regedit, and press ENTER.
Go to HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Services\CertSvc\Configuration\CA name\SubjectTemplate and correct the subject template string settings that you find.
Click Start, point to Administrative Tools, and click Certification Authority.
Right-click the CA name, and click Restart.