Q: I want to install an enterprise certification authority (CA) on one of my Active Directory (AD) domain controllers (DCs). Even though I'm logged on as a domain administrator, the option to install the CA as an Enterprise CA is greyed out in the installation wizard—it only lets me install a Standalone CA, as shown here. What's wrong here, and how can I resolve this?
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A: The problem is that you don't have sufficient privileges for writing the Enterprise CA configuration information in AD. To remedy your problem make sure that the account you use to install the Enterprise CA is a member of built-in Enterprise Admins group. For more information on the exact difference between Enterprise and Standalone CAs, see this Microsoft Technet article.