Why is this formula below not working as is?

If I remove either one of the conditions =$b$4 or <$b$5 it produces a value
but both conditions together it gives me 0 which is incorrect

Note: both b4 and b5 are '1000 and '1099 respectively


=SUMPRODUCT((ISNUMBER(MATCH('[YTDTB ACTUAL
''09-10.xls]YTDTB99'!$A$3:$A$277,$A12:$B12,0)))*('[YTDTB ACTUAL
''09-10.xls]YTDTB99'!$D$1:$CI$1=$B$4)*('[YTDTB ACTUAL
''09-10.xls]YTDTB99'!$D$1:$CI$1<$B$5)*('[YTDTB ACTUAL
''09-10.xls]YTDTB99'!$D$3:$CI$277))

Thanks