If you read the previous blog article (and were paying attention) you may have noticed that not only was there an unmonitored Management Server, but there were also two gateway servers which were in a grey state. These two gateway servers were the only gateway servers for a remote domain in the environment.
Reviewing the event logs on the gateway servers pointed towards the action account for the gateway server. In this case the password for the domain’s GWAA (Gateway Action Account) had been changed and resulted in the failure of the gateway servers. To resolve this I accessed the action account and changed the password to the updated one from the Administration \ Run As Configuration \ Accounts section.
Summary: If all of the gateway servers in a domain go to a grey state, verify that the user account and password for the Action Account are correct.