1. Make sure you have saved the output of the query as a selection and you have chosen to show the Selection in the Query Designer.
    Queries can only be available for other queries if their output is saved as a selection and that selection is . Please ensure that the output of the query is saved as a selection.
    User-added image
  2. Make sure the queries have the same source view.
    Selections of a query are only available in queries that share the source view.  Please ensure that the original query is in of the same source view as the query in which you want it to include the selection.