I was trying to add a new Windows 2012R2 Domain controller to an existing Domain. I was using the GUI tools, may be I should do this with PowerShell the next time. After adding the AD and DNS role I went through the DCPROMO wizard and kicked off the promotion. After a manual reboot I checked and all of DNS and AD seems to be working fine including replication. However, I’m still being prompted in the Server Manager to promote the server. When I do the following messages is displayed – “Error determining whether the target server is already a domain controller: The target server is already a Domain Controller.” After some research it looks like I’m not the only one, check out these posts. First thing always, run DCDIAG. The output only confirms that everything seems to be working. The solution seems to be to just disable/acknowledge the notification by clicking the “x” beside the task. Even after a reboot the notification doesn’t come up anymore.