SOLVED: HyperV – The IP address x.x.x.x you have entered for this network adapter is already assigned to another adapter

If you have moved a HyperV VHDx file to a new server, built a new VM using that drive and then tried to set the previous static IP Address on it, you will receive the following error:

The IP address XXX.XXX.XXX.XXX you have entered for this network adapter is already assigned to another adapter.

Usually I just click YES to:

Do you want to remove the static IP configuration from the absent adapter?

but today, I decided to dig in and simply remove the dead adaptor.  Fortunately this is quite easy to do:

1. Start a CMD prompt as an admin
2. Type: set devmgr_show_nonpresent_devices=1 and press ENTER
3. Type DEVMGMT.MSC and press ENTER
4. In Device Manager, click VIEW then SHOW HIDDEN DEVICES
5. Expand NETWORK ADAPTORS
6. Right click on each greyed out NIC and select UNINSTALL
7. Close all of the Windows (including your IP, Network and Sharing Center…)
8. Now try to change the IP and all will be happy.

If you want more details, see: https://support.microsoft.com/en-us/kb/269155