[SQL]Problème de requête insert

CREATE  FUNCTION getDureeProd(@groupId int, @nbSec varchar(8))
RETURNS varchar(10)
AS
BEGIN
	DECLARE @nbServers int
	DECLARE @nbSecInt int

	SELECT @nbSecInt = CONVERT(int, @nbSec)
		
	SELECT @nbServers = count(*)
	FROM Server
	INNER JOIN ServerGroup
		ON Server.GroupId = ServerGroup.GroupId
	WHERE     (Server.OutProdState = 0)
	GROUP BY Server.GroupId

	RETURN Convert(varchar(10), @nbServers*@nbSecInt)
END

INSERT INTO StatGroup (GroupId, GroupName, NbrSecProd, Mois, Annee, SumDelay, SumIncident, MTBF, MTTF, Dispo)
	SELECT 
		GroupId, GroupName,
		getDureeProd(GroupId,
			DATEDIFF(second,SUBSTRING(CONVERT(varchar(8), GETDATE(), 112), 1, 6) + '01', SUBSTRING (CONVERT(varchar(8), DATEADD(M, 1, GETDATE()), 112), 1, 6) + '01'))
		AS NbrSecProd,
		DATEPART(M, GETDATE()) AS Mois, DATEPART (YYYY, GETDATE()) AS Annee, 0 AS SumDelay, 0 AS SumIncident, 0 AS MTBF, 0 AS MTTF, 100 AS Dispo
	FROM ServerGroup

INSERT INTO StatGroup
                      (GroupId, GroupName, NbrSecProd, Mois, Annee, SumDelay, SumIncident, MTBF, MTTF, Dispo)
SELECT     ServerGroup.GroupId, ServerGroup.GroupName, DATEDIFF(second, SUBSTRING(CONVERT(varchar(8), GETDATE(), 112), 1, 6) + '01', 
                      SUBSTRING(CONVERT(varchar(8), DATEADD(M, 1, GETDATE()), 112), 1, 6) + '01') * COUNT(Server.GroupId) AS NbrSecProd, DATEPART(M, GETDATE()) 
                      AS Mois, DATEPART(YYYY, GETDATE()) AS Annee, 0 AS SumDelay, 0 AS SumIncident, 0 AS MTBF, 0 AS MTTF, 100 AS Dispo
FROM         ServerGroup INNER JOIN
                      Server ON ServerGroup.GroupId = Server.GroupId
WHERE     (Server.OutProdState = 0)
GROUP BY ServerGroup.GroupId, ServerGroup.GroupName