A new node couldn’t be inserted because one with the same name exists. (VERR_CFGM_NODE_EXISTS).
Found an understated bug online with exporting and importing Virtual Machines in VirtualBox, using the OVF 2.0 format.
Even though the error code has ‘NS’ in the title, which to me implies NameServer and therefore suggested a networking fault, the issue is actually in the USB Controller for the Virtual Machine.
Somehow the XML config file gets scrambled and VirtualBox cannot properly implement USB. This can be fixed by changing the USB implementation to another USB version, e.g USB2.0 to USB3.0. Then booting up the box works as VirtualBox has re-written the USB XML config file.