I installed a new PC recently with Windows 7 and successfully loaded the latest AirNav software. The PC was connected via HMDI 1.4 cable to a monitor. Alerts were setup with the message and emails. The PC is on 24hours per day and so the screen is turned off if I'm out. At that point the alerts cease. They are added to the alerts log but no messages and no emails. When I turn the screen back on, everything runs fine.
I emailed AirNav support and they had never heard of this either.
I then tried connecting the monitor using the DisplayPort cable and a separate audio cable to connect to the monitor speaker and the problem goes away and everything works as it should.
I thought to share this with you in case someone else is encountering this problem. I suspect that this may have something to do with the audio-return-channel that the HDMI cable has and DisplayPort does not and it would appear to be a software bug.
Cheers