Hello Adrian,
I could reproduce your problem now. It occurred when I stored the 'w7.vbox' file in the '/VirtualBox VMs/w7/' directory. Before, I had it stored in the root directory only and the problem did not occur. For running Windows 7 with VirtualBox on Nova we're using the 'virtualbox_auto_disk.run' script, which loads the '.vbox' file from the ROM service.
Regards, Christian