2003 buick regal

I have a 2003 buick park ave ultra with 40 thousand miles on it. 12 months ago i was on a 300 mile trip when my message center flashed on wiht service stabilty service system at about 250 miles of the trip. i did the reset procedure and it went off. after driving another 20-25 miles it came on again. i did the reset again and it went off. the following day i took my car to the dealerships service dept. i explained the above to the service mgr. and was told there was nothing he could do until the service stability system message was actually on. i do not drive this car very often, however last week i went on another 300 mile trip and at about 225 miles on the trip the service light came on. i did the reset and it went off. 30 miles from home it came on again. i drove home and took it to the service dept again. the service light did not come on and i explained this to the service mgr. they kept my car for two1/2 days and drove it several times, called me to pick it up because the light never came on. when leaving the light came on and i left it on so that they could see the actual light light on. would like to know why this occured.