Recently in one of our POC, we had problems installing agent a DC over a different site. A quick check on the physical server eventually found out that firewall is blocking the key ports thus communication could not be established. But then its a total different thing altogether.
We manually installed the agent from the DC and after approving it from OpsMgr console, the DC eventually got in as a Agent Managed Server. But hey wait a minute, how come the DC is not discovered with AD Role ???
The administrator insists that this is a DC.
Luckily Ray gave us a hint that it might be caused by AD Helper. We quickly went to the DC and check whether AD Helper is installed (though we should expect it to be installed automatically).
Apparently Active Directory Management Pack Helper is not installed and not available in Add/Remove Programs. So we need to install it manually, we need to go to the installation directory of the agent in the DC,
e.g. C:\Program Files\System Center Operations Manager 2007\HelperObjects
Launch OOMADS.msi and installation kicks in. Go to Add/Remove Programs to validate that the Active Directory Management Pack Helper is installed. Wait for a moment and voila' the DC will now have AD Role in OpsMgr console !