It’s already answered, but something easier worked for me (and without uninstalling VirtualBox):
“Go into Hyper V. Go into the Virtual Switch Manager. Create a virtual switch called ‘Windows Phone Emulator Internal Switch’. Make it’s connection type Internal.
Now launch the emulator. It should work.”
I had to reboot the machine before running the emulator, but now everything’s working fine: VS2012, Xde and VirtualBox.
Credits go to TheGeekNextDoor.