[Error] An item with the same key has already been added. I'm not sure what's happened

Hello everyone,

Just doing routine content updates and some macro started to error. I bring up ?umbDebugShowTrace=true and I'm getting this. (Full error in the link to pastebin)

Error Loading Razor Script (file: Royal Slider) An item with the same key has already been added. 
Server stack trace: 
  at System.ThrowHelper.ThrowArgumentException(ExceptionResource resource)
  at System.Collections.Generic.Dictionary`2.Insert(TKey key, TValue value, Boolean add)
  at System.Collections.Generic.Dictionary`2.Add(TKey key, TValue value)
  at Examine.LuceneEngine.SearchResults.CreateSearchResult(Document doc, Single score)
  at Examine.LuceneEngine.SearchResults.CreateFromDocumentItem(Int32 i)
  at Examine.LuceneEngine.SearchResults.<Skip>d__1.MoveNext()
  at System.Linq.Enumerable.Any[TSource](IEnumerable`1 source)
  at umbraco.MacroEngines.ExamineBackedMedia.GetChildrenMedia(Int32 parentId)
  at umbraco.MacroEngines.ExamineBackedMedia.<get_ChildrenAsList>b__8()
  at System.Lazy`1.CreateValue()

http://pastebin.com/cLqgkXy7

I've never seen this before, any ideas on what's happened?


This is a companion discussion topic for the original entry at https://our.umbraco.com/forum/47180-error-an-item-with-the-same-key-has-already-been-added-im-not-sure-whats-happened