With VMWare’s copying a virtual disk is easy: copy the disk in Windows Explorer and add it to a new VM; VMWare will detect that the disk was a copy and create a new unique identifier (UUID) for the disk before adding it to the VM. VirtualBox in this case isnt's so easy.
With VirtualBox, copying a virtual disk is a bit of a pain. If you copy the disk in Windows Explorer and try and use it in a new VM, VirtualBox will have a hissy fit and display the error shown below. A bit of a ‘wordy’ way to say that it already knows about this disk, don’t you think?
The VBoxManage tool will clone the disk for you, creating a new UUID in the process:
VBoxManage clonevdi source destination