Registry key permissions

I have a proprietary software application on an XP Pro workstation that downloads data from a locally connected serial device. According to the software tech, the registry permissions for the registry key HKEY_LOCAL_MACHINE\HARDWARE\DEVICEMAP\SERIALCOMM must be set to full control to work – and they are right. The problem is when the PC is rebooted, the permission revert to read. Any idea why this happens?