Because it can't do that.

Try:
=SUMPRODUCT(--(MONTH(range)=1),--(other_range=1))

--
Best Regards,

Luke M
"JP Ronse" wrote in message
...
Hi All,

New in Excel 2007.

Why is Countifs giving an error when I try to enter it with combined
formulas like:

=countifs(month(range);1;other_range;1)

With kind regards,

JP