Error: "System.IndexOutOfRangeException" logged in the Archive Manager Event Log for either FT (4336057)

An error similar to either of the examples below can be observed in the Archive Manager Event Log:

Source: FTIAttachmentWorker
EventID: 0
Description: AfterMail.Log.Configuration.ExceptionHandlerManager
[3403156645-881327888-1-0x0] The internal error happened:
There was an unhandled exception in this application

Exception Source: Lucene.Net
Exception Type: Lucene.Net.Index.MergePolicy+MergeException
Exception Message: Exception of type 'Lucene.Net.Index.MergePolicy+MergeException' was thrown.
Exception Target Site: Run
(Inner Exception)
Exception Source: Lucene.Net

Exception Type: System.IndexOutOfRangeException
Current User: DOMAIN\ArchiveMgr_Service
Application Domain: FTIAttachmentWorker.exe

___________________________________

Source: Full Text Index Service
Event ID: 2
Description: FullTextIndex.Indexer.Attachment: [4120737487-1147687945-1-0x0] Error performing attachment index
Exception Source: Lucene.Net
Exception Type: System.IndexOutOfRangeException
Exception Message: Index was outside the bounds of the array.

Exception Target Site: Get
Current User: DOMAIN\ArchiveMgr_Service
Application Domain: Archive Full Text Index Service.exe