Problem with my 95 Aurora

I have a 1995 Olds Aurora and i just got my oil changed last week and now my computer says oil level sys fault. I dont know what it means, i called the dealer and he said it might be low on oil but it was just chaged and i checked it and it is full, so i dunno what the problem is or what that means. I also shut off the car and restarted it and pressed the RCL buttom to see any problems and it said monitored systems ok, so i drove it for 10 minutes and than the oil level sys fault came up again, can u help me out?