DanCubitt

It could be the Valvetronic control unit got a bit mental and sending out loads of codes i doubt its the cat they are meant to get hot quick. get your car back from the indy find a second hand unit on ebay for about £70 and try that, easy job locate and unplug. if dont work sell it on and think again. i will find pic for you. Dont let them strip unless they are bmw specialist its a complex engine if you dont specialise in them .good luck