program staying in RAM after being closed

i have an application with System.timers.timer and threads. when i close my app, i call an event that kills off all threads and timers. but after the program is gone, i can still see it in RAM in task manager. i think its the timer as when i start my app a second time it say s object reference not initialised to object, and mentions the timer1_tick method. i have used timer1.dispose(), .close and .stop(), but it still does not work. when im debugging the project in Visual studio, this is not a problem. it just happens when use the release version. any ideas