While flying, my controller(older style serial port used with a usb adapter) loses it's calibration. I re-calibrate the controller which allows it to work normally for a minute or two, then it begins to lose calibration again. If I add some trim, it corrects the problem for a short while, but is just delaying the inevitable. I've tried calibrating the controller in both realflight and in the device manager. I have tried unistalling/ re-installing G2, but nothing has helped. I can't get through a single flight without having to calibrate the controller, and sometimes the calibration doesn't help. Any idea what could be causing this? I'm using Windows XP Professional.