* A virtual machine is no longer accessible from the network via RDP
* A virtual machine can only be accessed directly from the vSphere Console.
* The virtual NIC intermittently disappears from the Network Properties on your Windows guest operating system.
* The virtual NIC disappears from Inventory on the virtual machine’s Properties and appears to have been deleted.
ESX 4.x introduced a new feature called HotPlug. In some deployments virtual NICs can appear as removable devices on the System Tray in Windows guest operating systems. Problems can occur if you mistake this device for one that you can safely remove. This is particularly true in VMware View environments, where interaction with the Desktop is constant. Do not remove virtual NICs from the Windows System Tray.
For information about disabling HotPlug to prevent this issue, see http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=1012225