I have a customer whose IPO will reboot for no reason. They are 11.1 with two combo cards and are using the EXT O?P port for door closure. Normally a reboot/restart would not be noticed, in middle of the night, but door closure will unlock and allow entry until customer arrives and reactivates button on phone. Any idea what could be causing this? I have replaced all hardware ie Control unit, both combo cards and UPS.