Voltage Multiplier on Multisim

Hi,

I need to make a voltage multiplier in multisim, It's suppose to multiple 2 different voltages using 2 log op-amp, an adder, antilog op-amp. I have attached a picture of my circuit. So far I have tried changing resistor values, op amps, diodes to bjt method. But still none of the methods works. As seen from the picture my circuit works fine up to the point of the antilog op amp.I ran out of ideas on what might be the problem. Any suggestions and tips will be greatly appreciated.

Thanks.