Hello,

Thank you for your answer.

a and c are not whole columns and they have the same size.

For example:
a is worksheet1!A1:A15
c is worksheet1!C1:C15
b is worksheet2!A5

When I insert the SumProduct formula to worksheet cell it works. I get
an error only when trying to use it in VBA.

Can something else be wrong ?

Thank you
Gil D.