I was running out of disk space, so I needed to move virtual disk drive (VDI file) to another partition. As normally (read: in other virtualization tools) I removed/detached VDI file from virtual machine, moved it to new partition and added to existing virtual machine in this step error occurred:
"Failed to open the hard disk filepath.vdi
Cannot register the hard disk filepath guid because a hard disk different filepath.vdi with UUID guid already exists.guid
"
Solution:
Run following command "vboxmanage internalcommands sethduuid filepath.vdi"
PS vboxmanage.exe is normally located in "C:\Program Files\Oracle\VirtualBox"