The ASR (acceleration slip regulation) light is for the ETA (electronic throttle actuator) it is a mysterious beast that controls throttle placement. I would say that you have one of two problems. Either the interior insulation of the wiring of the ETA is is crumbling or the wiring harness is disintegrating. Either fix isn't cheap although if I had to pick one I'd pick the wiring harness. It's about a third of an ETA. In short check he wiring to the ETA, look for damage or water intrusion, if nothing is found you will have to replace the ETA control.
READ THIS POST FROM A M-BENZ FORUM MEMBER ON ASR ISSUE
For two years I lived with the the ASR light coming on shortly after starting the car and had to either continue driving it in the limp home mode, or stop the car to restart it to regain normal engine operation with the ASR light out. Finally, it got so bad I simply took a chance, after discussing the problem with a reputable local indie, and bought a rebuilt ETA from Potomac German Auto
and put it in. The part had a one year warranty with it and was about half the cost of a new unit from MB. There are other companies out there that rebuild these units as well. At any rate the ASR problem went away. To give you a reference point, my car had about 156,000 miles on it when I did this repair. That may or may not be significant to your situation, and I probably should have corrected this problem well before I did, but I didn't.