Thanks but, not working... your SQL
SELECT COUNT(*)
FROM history T1
INNER JOIN
(SELECT T2.HistoryID, MAX(T2.DateStamp) AS DateStamp
FROM history T2
WHERE T2.DateStamp<=[ParamDateStamp]
GROUP BY T2.HistoryID) T2
ON T1.HistoryID=T2.HistoryID
AND T1.DateStamp=T2.DateStamp
WHERE...