Peugeot 207 1.4 petrol depollution system faulty

[andymc1973 199]

Any experts on these? the car has had a full new exhaust (not cat) and the oxygen sensors look new, it's putting on the depollution light on start up and no more, cars runs fine, the machine says replace catalytic convertor, is this the general cause or a red herring, im just curious why the first place didnt change the cat?

 

thanks

Andy