SUMPRODUCT + DATE = 0
 

Hi,
I'm having this problem:
A B C
05-May-05 1000 -
06-May-05 2000 -
07-May-05 2300 -
08-May-05 1500 -
09-May-05 3600 10400
10-May-05 4100 -
....

I need to SUM periods like from 5 to 9 May in a column C, so I'm using:

SUMPRODUCT((A1:A100=DATE(2005;5;5));(A1:A100<=DAT E(2005;5;9));B1:B100)

The problem is: SUMPRODUCT = 0
am I doing something wrong??
Note that column A format is: DATE 18-Mar-98

Could you help me?? Thanks