Hi,
It works for me on my copy of Excel. Is there anything odd about the numbers - are any stored as text? What happens if you do =f4*A143*0.00001 instead of using the product function?
You could try removing each of the 3 arguments in turn to see if the formula resolves correctly. that is, if product(f4, A143) returns the correct amount, then you at least know the the formula has an issue with the 3rd argument. Once you know the one
that is tripping up the function you can look at that cell to see why. You could also try wrapping the arguments in value functions eg =product(value(f4), value(A143), 0.00001)
Regards,
Tony