Full Text Index Service Event Log error - Worker thread threw an exception (4219953)

The Archive Manager Event Log is showing errors similar to below, referencing an issue with the write.lock file.

Event Type: Error
Event Source: Full Text Index Service
Event Category: None
Event ID: 1
Date:  12/2/2013
Time:  5:24:46 PM
User:  N/A
Computer: ARCHIVEMANAGER
Description:
P9.P.0: Worker thread threw an exception
Lucene.Net.Store.LockObtainFailedException: Lock obtain timed out: NativeFSLock@C:\Quest Software\ArchiveManager\Index\Message9\write.lock
   at Lucene.Net.Store.Lock.Obtain(Int64 lockWaitTimeout)
   at Lucene.Net.Index.IndexWriter.Init(Directory d, Analyzer a, Boolean create, Boolean closeDir, IndexDeletionPolicy deletionPolicy, Boolean autoCommit, Int32 maxFieldLength, IndexingChain indexingChain, IndexCommit commit)
   at Lucene.Net.Index.IndexWriter..ctor(Directory d, Analyzer a, Boolean create, MaxFieldLength mfl)
   at Quest.ArchiveManager.FullTextIndex.Indexer2.OpenOrCreateIndex()
   at Quest.ArchiveManager.FullTextIndex.Indexer2.ProducerProc(Object context)
   at Quest.ArchiveManager.FullTextIndex.WorkerThread.ThreadProc(Object state)