The values in [Data.xls]Register!$B$2:$B$10000 are dates like 03/22/05

=SUMIF([Data.xls]Register!$B$2:$B$10000,MONTH(TODAY()-15),[Data.xls]Register!$AI$2:$AI$10000)
it just returns zero
im sure its the MONTH part thats messing it up, but i cant figure out a
solution

thanks in advance