When you add a network adapter to the host computer (including a Loopback adapter) the new adapter won't appear as an option on the Network Properties page for any virtual network, so you won't be able to connect a virtual network to it. To fix this problem, you need to enable the Virtual Machine Network Services driver on the adapter, as follows:

1. On the host computer, click "Start," click "Control Panel," and then click "Network Connections."
2. Right-click the connection that uses the new network adapter and click "Properties."
3. On the "General" tab, select the "Virtual Machine Network Services" check box, and then click "OK."

The network adapter should now appear in the "Network adapter on physical computer" list on the Network Properties page of any virtual network.

You can follow this procedure any time Virtual Server doesn’t recognize a network adapter. This is a rare occurance, but if there's already a virtual network configured on this network adapter, you'll have to remove from the virtual network any virtual machines that are using it and then re-connect them. Otherwise the virtual machines won’t have network connectivity. You do this as follows:

1. Open the Virtual Server Administration Website.
2. In the left pane under "Virtual Machines," point to "Configure" and click the virtual machine.
3. In the lower part of the page, click "Network adapters."
4. Click "Remove" and then click "OK."
5. In the lower part of the page, click "Network adapters," and click "Add Network Adapter."
6. In the "Connected to" box, select the network adapter to use, and then click "OK."