The vmxnet Network Adapter Device Status of a Virtual Machine Shows in the ESX Server System as Disconnected (1785)
Use VirtualCenter to manage a virtual machine with a vmxnet network adapter running on an ESX Server system.
Click Edit VM Properties > NIC > Device Status.
The Connected checkbox is always clear, no matter what the device status.
You can also fix this problem by upgrading to VirtualCenter 1.3 or later.