Sounds like boost cut.. but mate, PLEASE do not drive the car like that until you get it tuned.. or at least go back to the stock exhaust (or just cat back) until that time.

My wife's MY09 has an X-Force cat back that fits absolutely 100% perfectly, and has not thrown any CEL's or caused overboosting. The turbo back part is the bit that causes the problems with the ECU!