Devi spostare l'operatore WHERE sopra l'elenco dei progetti in cui viene creata la colonna RowNumber. Usa una tabella derivata o un CTE:
SELECT *
FROM (
SELECT *, ROW_NUMBER() OVER (...) as RowNumber
FROM ...) As ...
WHERE RowNumber = ...
il CTE equivalente è:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (...) as RowNumber
FROM ...)
SELECT * FROM cte
WHERE RowNumber = ...