Cannot register hdd ‘xx’ {nn} because a hdd ‘yy’ UUID {nn} already exists

You are cloning the virtual machine by copying the source virtual machine. When you reached the below step, Use an existing virtual hard drive file.

The following error, coming out,

Failed to open the hard disk file C:\Users\Admin\VirtualBox VMs\Clone\Clone1.vdi.

Cannot register the hard disk 'C:\Users\Admin\VirtualBox VMs\Clone\Clone1.vdi'
{9fc72b94-98e3-48ba-9444-6ef5a21a8c4a} because a hard disk
'C:\Users\Admin\VirtualBox VMs\Windows 7\Windows 7.vdi'
with UUID {9fc72b94-98e3-48ba-9444-6ef5a21a8c4a} already exists.

Result Code: E_INVALIDARG (0x80070057)
Component: VirtualBox
Interface: IVirtualBox {fafa4e17-1ee2-4905-a10e-fe7c18bf5554}
Callee RC: VBOX_E_OBJECT_NOT_FOUND (0x80BB0001)

Solution

Execute the following command,

VBOXMANAGE.EXE internalcommands sethduuid "<NEW_CLONE_VM_PATH>"

Example,

C:\Program Files\Oracle\VirtualBox>VBOXMANAGE.EXE internalcommands
sethduuid "C:\Users\Admin\VirtualBox VMs\Clone\Clone1.vdi"
UUID changed to: 2375050a-959e-419d-893d-6877ca32f180

Alternatively, you can refer to the article, How to Clone Virtual Machine in VirtualBox.