Volkswagen Polo engine management and epc light both on

I know lupo's are renowned for electrical niggles but this is takin the biscuit!! I recently replaced all sparks + leads together with a new battery only on sunday. (The engine light was on before this time) After fitting all the new stuff the light went off but the EPC light came on. It started and drove ok, but after 10 miles the engine management light came on again. I had this checked a couple of years back by VW and they couldnt find anything wrong with it. (yet they still failed its MOT on a water marked number plate!) Its beginning to become an annoyance for when we try to sell it and that thing is on! ive tried all sorts, oil changes, filters, the lot... i still cant find the problem!! HELP!

Dean