When you uninstall Exchange 2013, you might encounter the following error in the Event Log regarding the Managed Availability’s monitoring agent complaining that the server you uninstalled is not available:
Log Name: Microsoft-Exchange-ManagedAvailability/Monitoring
Source: Microsoft-Exchange-ManagedAvailability
Event ID: 4
Task Category: Monitoring
Level: Error
Description: Machine “uninstalled_server” has failed to heartbeat since “unistalled_date_and_time”, as observed by machine “some_other_server”. Restarting the Exchange Health Manager service did not fix the problem.
The problem is that the old server continues to be present under the following registry key for all other Exchange Servers:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\ExchangeServer\v15\ActiveMonitoring\Subjects
This causes the error above in the Event Log or SCOM alerts. If this happens, the workaround is to simply delete the old server(s) from the registry key mentioned above on the remaining servers.
Microsoft says that this bug was previously closed as Won’t Fix but that they have re-opened it for re-triage.
