Esta es la respuesta correcta !!!
Código SQL
[-]CREATE PROCEDURE Extra_calculo_diaferiados
@fechaI datetime,
@fechaF datetime
AS
SELECT A, B, C, sum(D) as Dias, sum(O) as Cobrar
FROM Tabla
WHERE (fecha between @fechaI and @fechaF)
GROUP BY A, B, C
ORDER BY A, B
Muchas grasias amigos !!!