Sumproduct Error

Hi --

Need your help in rectifying the formula I'm using.

=SUMPRODUCT(SLVL!$B$6:$B$49>=$A$2)*(SLVL!$B$6:$B$49<=$B$2)*(SLVL!$A$6:$A$49=A12)

I'm sure that there had been an error somewhere but I can't figure it out. I'm getting zero value.

Situation: need to count number of leaves within a specified period, thus I opted to use Sumproduct.

Thanks in all advance!

Mike