A few days ago, the SRS light popped on the E55. When I purchased the car, this light was illuminated for unknown reasons, but it was cleared and off for the better part of four months after it spent a week at my shop in Rhode Island.
Now, I'm a week away from getting it inspected here in Maryland and the SRS light pops on (because of course it does.) After reading numerous old forum posts, the consensus seems to be that the Foxwell NT530 scanner and code reader - a Chinese made device with virtually no customer support - is the way to go, especially since they sell it with Mercedes-specific coding and a 38 pin connector for attaching to the car via the fuse box.
I got it from Amazon for about $200 and gave it a whirl today. Historically, getting rid of an SRS fault code has been quite tricky, with most owners telling folks in this predicament to suck it up and go to the dealer; thankfully, my code was wiped clean with ease, so kudos to this Chinese-made scanner for building a product that actually works and saved me a trip to the shop.