Boostjunky

HI guys,
Picked my car up from the clutch and flywheel being changed on friday night, the cars an 03 Impreza Sti UK PPP with a 3inch system and headers remapped to around 340 bhp, (no decat). After about 40 miles of driving it chucked up the CEL on saturday afternoon. I've been under and checked the 02 sensor after the cat connections look ok and no evidence of any damage to the wiring. My car had a remap at powerstation about 3 weeks ago and everything was fine, smooth strong power band and everything as it should be. Car drives fine, still pulls strong but going into boost is a little lumpy. The CEL is also still on after 5 restarts some from cold. Not driving the car now but would appreciate some ideas to throw at the guy who did it as he's gonna dance around this having something to do with what he's done, he's already gotta explain a dent on my wing, had prodrive springs installed while it was in and the dent on the wing lines up perfectly with the shocker where he would have been working. Any ideas would be much appreciated as I would like some verbal ammunition to give this guy an early morning railing tomorrow. Would also like to add this was no backstreet garage but my local subaru specialist who only works on subaru's and after paying just under a grand and i'm not happy that my car remains unusable with a nice new dent for garnish.
cheers guys from ross