Selection sur les dates

Salut
j'e doit retourner des enregistrement entre 2 dates mais je n'arrive pas à utiliser la borne superieure,

quand je met e une borne superieur les resultats sont vides, avec la borne inferieur je n'ai aucun probleme

Code:

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	SELECT 
		perimetre,
		societe,
		id_pole,
		pole,
		SUM( IF(id_avancement=8,1,0)) as N1,
		SUM( IF(id_avancement=9,1,0)) as N2,
		SUM( IF(id_avancement=10,1,0)) as VN,
		SUM( IF(id_avancement=11,1,0)) as CAR,
		SUM( IF(id_avancement=7,1,0)) as CS,
		SUM( IF(id_avancement=7 AND (classe_ecole=1 OR classe_ecole=2),1,0)) as CS1,
		SUM( IF(id_avancement=3 OR id_avancement=5 OR id_avancement=6 OR id_avancement=14 ,1,0)) as Resil,
		SUM( IF(id_avancement=13,1,0) or if( (DATEDIFF(NOW(),date_avancement )>10 AND id_avancement not in (3,5,6,14,7,11)),1,0)) as attente
	FROM TEMPO_STAT
--		WHERE date_avancement BETWEEN 2007-01-01 AND 2007-12-31
	WHERE 
		date_avancement > 2007-01-01 
		AND date_avancement < 2007-12-31 
	GROUP BY id_pole
	ORDER BY id_pole

merci