When installing a replica domain controller I get ‘Could not retrieve domain controllers. External component has thrown an exception’ By Mariette Knap replica domain controller, Could not retrieve domain controllers At some point during any migration project, you are going to install a replica domain controller. During the installation of ‘Active Directory Domain Services’ you are presented with a task called ‘Promote this server to a domain controller’. But if you did not raise Forest functional level of your original Domain Controller you get ‘Could not retrieve domain controllers. External component has thrown an exception’. Tip: In addition to this procedure, you may find that you need to add the user to the Schema Admins and Enterprise Admins security group. But then you get this error ‘Could not retrieve domain controllers. External component has thrown an exception’ If this happens to you the first time I can imagine you have absolutely no idea what to do with this error but the solution is easy. Upgrade the Forest Functional level to the highest available on your original Domain Controller and here is how you do that This procedure is done on the original Domain Controller. From the start menu choose Administrative Tools and then Active Directory Domains and Trusts. Right click and choose Raise Forest Functional Level. If you don’t see ‘Raise Forest Functional Level’ but you see ‘Raise Domain Functional Level’ you have chosen the wrong level, chose the highest level. In the dropdown box it should mention ‘Windows Server 2008 R2’ and choose raise. Accept the warning and click OK. Click OK