When accessing a resource mailbox in Exchange 2013 EAC, you may encounter an error that you prevents you from viewing or editing the room mailbox properties:
Powershell is no good either!
WARNING: An unexpected error has occurred and a Watson dump is being generated: The value ” is already present in the
The value ” is already present in the collection.
+ CategoryInfo : NotSpecified: (:) [Get-CalendarProcessing], InvalidOperationException
+ FullyQualifiedErrorId : System.InvalidOperationException,Microsoft.Exchange.Management.StoreTasks.GetCalendarProcessing
Cause: Typically this is because there is a disabled mailbox listed in the RequestInPolicy or BookInPolicy attributes for the room.
Solution: Run the following in Exchange Powershell to clear the values. Example: Set-CalendarProcessing <Room> -BookInPolicy $null
Once done, you should be able to access the room via Powershell or EAC and re-add any required requesters to the room policy. Alternatively, if you have Exchange 2010 still around, you can simply remove the disabled mailbox via the 2010 EMC.