I had an issue with resizing a Virtualbox .vdi file.
Command used:
vboxmanage modify disk.vdi –resize 40960
Error displayed:
VBoxManage: error: Cannot register the hard disk ‘disk.vdi’ {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} because a hard disk ‘disk.vdi’ with UUID {xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx} already exists
Solution:
vboxmanage modifyhd {abc03a41-794b-4a84-adaf-789436919417} --resize 40960 (e.g 40gb hd)
replace {abc etc with the correct UUID
See the link below for more detail and the solution.
http://amapplease.blogspot.com.au/2011/10/resizing-existing-hdd-image-in.html