is the c3 reference in the first cells in the current page or the GDOS page?
are the B column data actually values or could they be numbers as text.
a quick check is to run each segment separately
=sum(GDOS!$B$3:$B$10000)
=SUMPRODUCT(--(GDOS!$C$3:$C$10000=$C3)) or
=countif(GDOS!$C$3:$C$10000,$C3)

"MESTRELLA29" wrote:

=SUMPRODUCT(--(GDOS!$C$3:$C$10000=$C3),GDOS!$B$3:$B$10000)

This formula is trying to work as a VLOOKUP for text "1C"

Right now the result of this formula is 0, does anyone know why and how can
I correct this?

Thanks