How about this?
SELECT Force_No AS FN, Subs_Dt, Subs_Amt,
(SELECT Sum(a.[Subs_Amt])
FROM GIS_Subs AS a
WHERE a.[Force_No] = GIS_Subs.[Force_No]
AND a.[Subs_Dt] <= GIS_Subs.[Subs_Dt]) AS dblRunningTotal
FROM GIS_Subs
ORDER BY Force_No, Subs_Dt;
You will have to be...