Readynas Ultra 2 - Mac Address became 00:00:00:00

Hello,

I stopped my nas for few days during holidays and when i restarted it i couldn't access it.
I finally managed to connected it, and i noticed that no correct ip was assign by my router to my nas. This is because the Eth0 has now a 00:00:00:00:00 mac address. I tried a os reinstall but it is still the same. I managed to force the mac address to his old mac address (using ssh and ifconfig) and the ip was assign successfully by my router. But if i reboot the nas the problem come back.
And I noticed too that since today i can only access my nas come from outside but not coming from the local network.

Does anybody has any ideas?

Thanks in advance, and happy new year 2015!