=SUMPRODUCT(--(MONTH('2008'!B3:B2000)=1),--(YEAR(B3:B2000)=2009))

Hi all, I am using the above, but am getting #VALUE!

The format the date is typed in, in the main data sheet, is "05 January
2009", but I have also tried 05/01/2009 but to no avail. Can anyone say
where I am going wrong?
Thanks
Tina