agrupar por hora o devolver la hora de una fecha

[Rocket]

sip, este es el sql

SELECT CONVERT(nvarchar(2), dFecha, 108), count(id) as cantidad
FROM Error500_Detalle
WHERE day(dFecha) = 5 and month(dFecha) = 9 and year(dFecha) = 2006
GROUP BY CONVERT(nvarchar(8), dFecha, 108)
ORDER BY year(dFecha), month(dFecha), day(dFecha)

y este es el error
Column 'Error500_Detalle.dFecha' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.
Column name 'Error500_Detalle.dFecha' is invalid in the ORDER BY clause because it is not contained in either an aggregate function or the GROUP BY clause.