Do you have some domain controllers that are appearing in a Not Monitored state? If so, while there can be several reasons why an object would have a Not Monitored state, below are two very common reasons why a domain controller appears in this state if you are running the Active Directory Management Pack:
1. The domain controller does not have an agent installed.
2. The domain controller has an agent installed but it doesn’t report to this Management Group.
There is an option to remove these domain controllers that appear in a “not monitored” state and you can refer to the Active Directory Management Pack User Guide for details on this.
For a more in-depth look in to this issue see Domain Controllers not monitored state on my blog.
Download the Windows Server Active Directory Management Pack for Operations Manager 2007, including the User Guide.
Jonathan Almquist | Microsoft Premier Field Engineer