ok go it to work. thank you pbaldy for your help
here's the query.
SELECT qryMerge.FileName, ConcatRelated("Categories","qryMerge","ClipID = " & [ClipID] & " AND ActorsID = " & [ActorsID]) AS Categories
FROM qryMerge
GROUP BY qryMerge.FileName, ConcatRelated("Categories","qryMerge","ClipID = "...