Arduino Duemilanove & Nano --> LM35

Hello All,
I’ve installed on arduino nano the following code:
(http://playground.arduino.cc/Main/LM35HigherResolution)

Unfortunatelly it show me a very floating result and a temperature from 90 to 120° C…

I’ve installed the same sketch on an arduino Duemilanove and the result is fine every loop it shows the same result (±0.5°), and the result is consistents, about 26° C.

Someone could explain me why this occours and how can I workaround the problem?

Many thanks

Schematic on both cases nedeed to help.
Did you investigate about aRef 1.1V on both boards? This may be the issue, atlhough i don't know if this depends wether on the Atmega328P or some board connection.