“The IP address x.x.x.x you have entered for this network adapter is already assigned to another adapter…” when assigning a NIC’s IP address.

While this informational message can be caused by various reasons, here’s the list that I could think of off the top of my head:

1. You’ve just completed virtualizing a server to a virtual machine and new NICs were created replacing the old ones.
2. You’ve physically removed NICs from a physical server and replaced it with new ones.
3. You’ve just completed the installation of MSCS (Microsoft Clustering Services) within a VMware VI3 environment and you noticed the IP addresses are gone so you make an attempt to re-enter them only to get this message.

There’s probably more but those are the ones I can think of now. Earlier in the days when I was a cowboy and pretty much hacked away at everything, I used to just go into the registry and delete all the keys with the IP address that was assigned to the old NIC before I went ahead to re-enter it into the new ones. This worked but searching through the registry and constantly hitting the F3 key for Find Next is cumbersome and prone to human error. The easier way to fix this is to actually use the following KB: http://support.microsoft.com/kb/315539 to reveal the hidden/missing adapters and uninstall it. This provides a much cleaner method of cleaning this missing adapter out.