Sometimes after a P2V conversion or after recreating a VM and re-attaching the original hard drive, the drivers for the old physical NIC are still present and the physical NIC is still considered by Windows as a device on the machine.
The problem with that is that the original NIC will be ‘hidden’ somewhere in the system configuration and you'll be unable to assign the IP address to the new NIC because it is still bound to the old NIC.
In this situation Windows will come up with its annoying popup error message:
"The IP address x.x.x.x you have entered for this network adapter is already assigned to another adapter."
If you look in the list of devices in Device Manager you will notice that your new NIC is now listed as “Microsoft Virtual Machine Bus Network Adapter #2” and that no other NICs are apparently present in your system. So where is NIC #1? Well, it's still there but it is hidden and as long as Windows remembers about it you will not be able to assign the new NIC its correct IP address.
To get rid of the old ghost NIC, follow this simple procedure:
1.Click Start > Programs > Accessories > Command Prompt.
2.Type the following command and press Enter:
3.Type the following command, and press Enter:
Make sure you type devmgmt.msc in the same Command Prompt where you typed "set devmgr_show_nonpresent_devices=1". This is because the "Set" command is only effective in the environment of the Command Prompt you opened and its setting will be cleared when you close it.
4.Now in Device Manager click View > Show hidden devices.
5.Expand Network adapters. The old physical network cards are now visible and grayed out.
6.Right-click on these NICs and click Uninstall.
At this point you can assign the IP address to the new virtual NIC.
Just a last note: as a Windows Active Directory administrator, and for ease of management, I suggest to set this environment variable globally via Group Policy and to push it down to all your computers. To do so define a new GPO that will put in place the following registry key:
System Key: [HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\Session Manager\
Value Name: DEVMGR_SHOW_NONPRESENT_DEVICES
Data Type: REG_SZ (String Value)
Value Data: (1 = show all hidden devices)
A reboot will be needed for the registry key to be applied. I am sure that doing this via GPO will save you a lot of time, because old hidden NICs are a common and recurring problem in Windows environments and being able to uninstall them without going through a too long procedure is a major improvement to me.