Last night, I rebuilt my Windows Server 2008 machine at home to use the RTM build (it was running on an escrow build from a few days before it was finally released) and Hyper-V RC0. The recreation of the virtual machine configuration (but using the existing virtual hard disk) meant that Windows detected new network adapters when I started up the VM. Where I previously had a NIC called Local Area Connection using Microsoft VMBus Network Adapter I now had a NIC called Local Area Connection 2 using Microsoft VMBus Network Adapter #2. When I went to apply the correct TCP/IP settings, a warning was displayed that the IP address was already assigned to another adapter. In a physical environment, I could have reinserted the original NIC and uninstalled the drivers, but that was less straightforward with virtual hardware.
I tried getting Device Manager to show the original adapter using set devmgr_show_nonpresent_devices=1 start devmgmt.msc but it was still not visible. As described in Microsoft knowledge base article 269155, I ran devcon to identify the phantom device and then remove it. After identifying the identifier for the NIC, I used:
devcon -r remove "@VMBUS\{20AC6313-BD23-41C6-AE17-D1CA99DA4923}\5&37A0B134&0&{20AC6313-BD23-41C6-AE17-D1CA99DA4923}"
Note: the devcon package from KB311272 includes versions for i386 and IA64 but not x64. For 64-bit, devcon is one of the Support Tools on the Windows installation media (suptools.msi).