It seems that the new node/configure node page does not correctly poll the list of machine names. I had to restart vboxwebsrv a couple of times since I tried to have it run as a windows scheduled task. At some point, I had the cloud already configured and tried to configure the existing node or create a new one and although the VirtualBox Host field was filled correctly, the Virtual Machine Name list was empty. It did cost me a couple of hours, reboots and restarts to figure out that when I just saved the node without a machine name and then edited it again, the machine name suddenly popped up.
Sorry if this might be the wrong component to post this. Not really sure if this is a a problem of the plug-in or Jenkins in general, I'm just starting to use Jenkins and find my way around...
Jenkins 1.480 running on a Windows Server 2003, VirtualBox 4.2, Virtual Box Plugin 0.5.0, FireFox 15.0.1