Under Tools | Manage | Recurrence Settings in the MessageStats console, there appears to be a number of entries for Gathering Server and some are duplicated.
When I try to add an Exchange Server to either the Interactive or Automated gatherings, I receive a message stating that the server is being handled by another Console or Process.
This indicates that Exchange Servers from other consoles in the environment were not removed after they had been decommissioned.
To resolve the issue delete (not clear or remove) the entries in the following tables in the MessageStats database:
Now open up the MessageStats Console and you will be able to configure the Exchange Servers for gatherings and won't have duplicate gathering servers under Recurrence Settings.