BMW of N. America sent out a notice dated December 2008 about the failure of the "passenger seat occupant detection mat." When that happens both air bag warning lamp and the passenger air bag "on-off" lamp will illuminate and the passenger side air bag will not deploy. They recommend that the vehicle be serviced promptly and that passenger seat not be used until the problem is corrected. BMW N. America provides an extended warranty for this defect for ten years from the in service date of the vehicle.
Also mentioned in the 2008 article from USA Today .