I recently went to a staggered tire size front/rear and am currently rolling on a 205/55 16 front and a 225/60 16 rear - problem began when I mounted the front tires.

I know the rear is at the absolute maximum diameter or at least visually very much fills the wheelwell -

Could the ASR system be faulting out based on the substantially different tire sizes front/rear?

 

Most deffinitly. Wheel/tire size makes all the differance because the systems are programmed to oem specs for wheel size. If you want to go staggred call a mb dealer and have parts quote a staggred tire size for your specific vin. Don't buy just compare to what you have on your car