I had the same thing. Take it to your dealer, he will connect the diagnostics computer to the airbag system (it's got separate tests for that system), and it will find out where the problem lies. On mine it was a problem with the seatbelt pretensioner on the driver's side (same system I think). You should get it fixed though, and fast, because when that light is on it means all the airbags are disabled, as far as I understand.
ps! no traces on my car after they fixed it, everything just works now!