This was a weird one. I’ve just built the new x64-based VM server, and moved a number of my VMs onto it for testing. A few of those VMs run under a local (to the host) service account so they can be automagically started by the server. For some reason, the VMs which had been set up like this couldn’t see the External network. I reinstalled the VM Additions, removed and reinstalled the NIC in the Guest and generally scratched my head because this same setup worked just fine when it was a 32-bit box and it was exactly the same… wasn’t it?
Well no, actually, it wasn’t. Turns out the user I’d created for launching the VMs on the x64 box wasn’t exactly the same as the user on the old box. It wasn’t a member of the Administrators group. So note to self: if you want them to be able to access the NIC, start your VMs in a user context that has Admin rights. I’m sure with a bit of testing I could find the URAs that would lock this down with a little more granularity, but the Administrator right blanket fits for now!