ZFW always 0 in CDU

I am having trouble since updating Boeing CDU. In the Perf Init page after I enter the fuel quantity, reserve etc I press the ZFW and it calculates as zero (0.0). In previous versions this would automatically enter the zero fuel weight of the aircraft. I have tried different aircraft types but they all do the same. I obviously haven't set something up in my config files but I can't see what needs to be done. Anyone able to help please.

Hi

Just type the ZFW in, like in real.

Thanks Thomas
I thought this would be the answer but in past times it was automatically entered when I pressed the LSK. Entering manually works fine.