My daughter drives an Explorer that had the same symptoms. She set and released the ebrake several times but light still went on occasionaly. Since she lives out of town, I called a mechanic friend. He said the brake fluid was probably low...just check it and fill it since it is on the same system as the parking brake. She did check her fluid and it was low. She bought a $2.00 pint of dot 3 fluid, topped it off and everything was fine.

Hope this helps.