Not monitored state on Operations Manager Agents or Management servers

It is very common to see  agents or management servers in a not monitored state.

Following is a great post by SCOM Engineering Blog which shows out a bunch of reasons for this to happen.

http://blogs.technet.com/b/momteam/archive/2008/03/10/getting-headaches-trying-to-figure-out-why-you-are-seeing-the-not-monitored-state-for-management-servers-or-agents.aspx