Brake Sensor Light on Dash

About four weeks ago the red brake light (the one on the instrument panel that comes on when you set the parking brake) came on. Since the brakes worked and the fluid level was fine, I didn't get too concerned. Well over the past four weeks it sometimes comes on and sometimes doesn't. The most annoying part is that is overrides the cruise when it comes on. I took it to a mechanic and he said everything looks fine and he topped of the brake fluid reservoir. However, the next day driving down the road it just randomly came on again and popped off the cruise. I suspect possibly a bad sensor or loose connection, but I would appreciate any help anyone could provide regarding this issue.

Did your ace mechanic check the parking brake switch for continuity to ground when engaged and open when disengaged?

Try making sure parking brake is fully retracted....The best time to test this is of course when the light is continually lit....