When you are creating a new virtual machine in Hyper-V, you might see an error resembling this:
“Microsoft Synthetic Ethernet controller couldn’t be used”.
(Note: you might run into a bunch of other errors that are related, as well)
If you see this error, it basically means “game over” as your VM will be “broken” before you’ve even started it.
One evildoer that causes this error is Trend Micro. I first read about it at Technet; and verified it myself: Trend Micro can cause this problem.
How to fix the problem:
Fixing this problem is pretty simple:
1) Disable all Trend Micro Services OR temporarily unload the Trend Micro Client Agent on your Hyper-V server
2) Attempt creating the virtual machine again. It should now work fine.
3) Once the virtual machine is created, restart the services / load the client agent again.