====== How to duplicate a vdi ======
You cannot simply copy the dir containing the vdi drive and the other files because every machine must have a unique ID.
There is a special command for this purpose

On Linux
<code>
VBoxManage clonevdi fileorig.vdi filetarget.vdi
</code>

On Windows
<code>
<appdir>\VBoxManage clonevdi fileorig.vdi filetarget.vdi
</code>
<appdir> is generally c:\program files\VirtualBox.

What if the file is already copied without that command? You can assign a new ID to make it works as well even if you didn't use the clonevdi command.
<code>
VBoxManage internalcommands setvdiuuid "filetarget.vdi"
</code>