I discovered that my F920BT worked perfectly and didn't restart (reboot) when I started the car. 

It never had updated the firmware, but today I updated the firmware to the latest version (2.00300) published by Pioneer.

My surprise was that after the firmware update my AVIC F520BT restarts (reboot) when I turn on my car.

How can I do a downgrade to know if the error is the firmware ????

Has someone had the same error ????

Thanks.

Is it possible you let your battery run-down some during the install? 

My Z110BT used to always reboot when it was playing as I restarted the engine. Even with a new OEM factory battery. Last month I needed a new battery again and I bought an AGM with 900 CCA. Now it always keeps playing when restarting.

So maybe your battery's residual power drained just enough (during f/w installation) to cause a reboot when the volts dropped while cranking. Try putting the car on a charger/maintainer overnight, or taking an hour-long drive. It takes the car's alternator quite a while to fully charge a battery. 

BTW, I really doubt this is a software issue.