I finally knew the problem.
I tried changing my domain name in System>General Setup.
But when I checked with my PC and the scanner machine, the domain name was the previous domain.
I did an ipconfig/flushdns, restarted the NIC of my PC but still the same.
So I checked with the DHCP server, under Domain name, I specified my previous domain name.
Even if I change the domain name, I always get my previous domain.
I empty the box under Domain name, did a flushdns and restarted the scanner and everything is now ok.
I still don't get it how that option affected my LAN.
Anyway, thanks to all especially WALLYBOB for helping me with this.