Perhaps this solution might work as well (http://www.subaruoutback.org/forums/66-problems-maintenance/42574-2006-obw-airbag-light-my-fix.html )If the light in overhead /maplight is out it will cause the light to come on in your dash, this is a common fault that I have come to know when mine did the same. It is a safety issue and if not possibly not deploying the SRS.
The only way is to replace your overhead/maplight with a new one. . . .
Had this problem with my 2008 OB XT. Re-soldered the "off" light, works like a charm. Airbag fault light hasn't been on since. Thanks forum! Saved me hundreds...I presume you mean that the "Air Bag" warning light in the instrument panel (combination meter) is on.
There's another seat belt warning light in the overhead panel above the rear view mirror. This one indicates when the right front passenger air bag is being armed (active) or not (off). This will usually change from off to on when someone sits in the seat.
There have been cases where a bad solder joint in the printed circuit board that the overhead panel lights are mounted to will cause the Air Bag warning light to come on. The air bag diagnostics system checks the connections to the lights, and if one is bad, it disables the Air Bag system, and turns on the warning light in the instrument panel.
This thread has the same apparent problem as you. Look at the second link in post #5; it has more details about the printed circuit board and the bad solder joint.
Not saying this is your problem, but it might be. The best approach would be to first narrow down the area by having the airbag trouble code read. The code will indicated where the problem is, at least in terms of which circuit. If it indicates the light then the linked threads could have the solution. If it indicates a problem in one of the air bags themselves, it would be something else. In this case it could be a loose connector, or something else.
Not sure if the is any way to read the SRS Air Bag codes without going to the dealer, but read through the threads -- someone might have posted a method that I'm not aware of.
Hope this helps; let us know . . .