Du kan ikke bruge aliasede kolonner i en WHERE
klausul. Du kan prøve at bruge en afledt tabel. Måske noget som dette (undskyld, ikke testet):
SELECT * FROM
(SELECT SQRT(POWER(cast(Program_Latitude as float) - cast('41.5126237' as float), 2) +
POWER(cast(Program_Longitude as float) - cast('-81.6516411' as float), 2)) * 62.1371192
AS DistanceFromAddress from tblProgram) mytable
WHERE DistanceFromAddress < 2