I have a similar experience when I sent my car to the paint shop to change the color of my spoiler. My in-car message indicated : "Air brakes failure, return to Mclaren dealer"
Installation of the exhaust would most likely require removal of the spoiler and rear engine compartment hatch. There are several electrical connectors that could have been detached and reattached during the installation whilst the car did not go into a total 'shutdown' mode.
You need to sent your car back to the dealer to reset those sensors.
Indeed Spar did you try and hold the aero button. While driving I must have accidentally pushed the aero button and the wing was standing upwards. Held the button several seconds and it came down.
Since the, I pay attention. Last week the wing was standing upwards when parked. I simply drove off and it came down. No errors.. At least not the air brake
I am getting Airbrake failure warning with the "!". Could not remember to hold the Aero button for 5 seconds. Drove the car with Aero up, came down when I drove off. Drove the car a second time for about 10 miles, when I was about 2 miles from home, the error warning occured. My airbake is down, but when I try to press Aero button, it will not light up.