Yeah, wasn't sure which one it was that you were on about.
Usually, and I could be wrong, that light coming on means the battery is low, isn't getting enough charge or is being drained more than it's been charged while the engine is running. Happened to my Omega all the time but that was due to the fact that I hardly drove it and once it had had a good run it would go away. Seemed to always come back in the winter when I had my lights on all the time.
Check the clock diagnostic and see what voltage is coming off. If it's 14v ish then I'd assume the alternator is ok.