Cannot register the hard disk uuid already exist

I was trying to copy the previously installed vdi file that has installed Win10, but get this error when trying to create a new Virtual Machine with the new vdi file as the disk.

Looks like for each virtual disk, VirtualBox will write an UUID into the file, but what's the point? Why the virtual disk file has to be unique? Imaging what it feels if you can't copy a word document and open the file and the original document in Microsoft Word at the same time.

Execute the following command to change the UUID of the vdi file

C:\App\virtualbox>VBoxManage.exe internalcommands sethduuid "i:\VirutalMachine\win10envs\win100.vdi"
UUID changed to: 5eb050e1-efb1-4793-acae-05afb8a3fa2e

The method is useful when you already copy the file directly. The better solution is using the copy feature of VirtualBox Manager, not copy files in the OS. It will handle the UUID problem for you.