91 - Check Oil light

I have a 91 Buick Park Avenue. I bought the car last year and it has been parked in a garage for a little under a year. I had a mechanic check it over and replace all the fluids, oil, and filters. I noticed that my Change Oil Soon light is on. I followed the directions in the book with reseting the system by holding in the switch for five seconds. I do this and the light blinks four times and goes out. However a few seconds later the light comes back on. I've reset it about 10 times with still no luck. Does anyone have any ideas what it could be??

Thanks in advance.

What oil pressures are you getting on your oil gauge at idle and around 3000 rpm?

At idle the guage reads about 60 and at 3000rpms the guage reads about 80.