I have the same problem with a 98 528i, the airbag light stays on. Also other goodies happen, the stereo works when it feels like it and the steering wheel will periodically move up and down. This provides great entertainment for the kids but it is all very annoying and concerning. I had this fixed before about a year ago and the dealer fixed it for a minimal charge. It had to do with the front seat belt tensioner, I believe it was a bad connection. I will check the connection myself this time before bringing in for service.