You'll get that error message when the Realtek 8111F Gigabit LAN Controller chip is not being detected by the Operating System.
Have you tried powering down the system completely? Actually turn off the PSU's AC power switch or remove the AC power cord for half a minute or so and then plug it back in or turn the AC power switch back on.
Check the following BIOS setting:
ASUS UEFI BIOS Utility - Advanced Mode
Advanced ====> Onboard Devices Configuration
Realtek LAN Controller [Enabled]