Debe mover el operador WHERE arriba la lista de proyectos donde se crea la columna RowNumber. Utilice una tabla derivada o un CTE:
SELECT *
FROM (
SELECT *, ROW_NUMBER() OVER (...) as RowNumber
FROM ...) As ...
WHERE RowNumber = ...
el CTE equivalente es:
WITH cte AS (
SELECT *, ROW_NUMBER() OVER (...) as RowNumber
FROM ...)
SELECT * FROM cte
WHERE RowNumber = ...