I've recently acquired a 515E with PIX software version 7.0(1). I've noticed after an indeterminate amount of time (5 minutes to hours), the PIX will reboot itself. When this happens, it usually takes a few tries for it to successfully reboot, but it does eventually. I've tried going back to the factory-default configuration (config factory-default) but it still exhibits the same behavior. Any ideas? Or is this just a defective unit that I need to get replaced?