Under the conditions you reported, the ABS system needs to be serviced. It is indicating that your ABS is not working, but as long as the brake light is off, you still have regular brakes.
I suspect that one or more of your wheel sensorshas either shaken out of alignment, orhas failed. Personally, I would be headed to my nearest dealer for service, especially now that winter driving is nearly upon us ....
note: edited to correct poor spellingEdited by: OceanArcher
before servicing it remove the battery cable so there is no power to the car, leave it that way for a good 5-10 minutes, plug the batter back in and start the car, take it for a test drive to see if the light comes on, if the light comes back on may as well keep driving it straight to a garage, might havea leak in the lines, might be low in fluid, might be alot of things... may as well get it checked out though