Found this on a mercedes site.
Just solved the tow away problem this weekend.
Was a damp pse.
Took the pse out, removed cover, dried her off with a hairdryer for about 2 hours, cut the vac lines, added a foot to each, flipped upside down in trunk now.
Since I removed the cd changer I used one of the leftover screw holes for a brace to hold the pse is place.
No more tow away light and car is happy girl again =)