virtualbox no puedo eliminar un viejo snapshot

 Me encuentro este post de un tío que sabe:
http://nicolasjolet.blogspot.com.es/2012/02/virtualbox-not-allowing-to-delete.html

 Lo copio aquí tal cual:
 
 Traduzco, la opción está en /Archivo/Admistrador de medios virtuales ---> Despliegas  y de los que sale le das click con el botón derecho del ratón para ver opciones, y en el que te aparezca la opción de borrar, pues eso, borra.


Today I got an error while trying to delete a VirtualBox snapshot :

"Failed to delete the snapshot XXXX of the virtual machine YYYY" (english)
"Échec de la suppression de l'instantané XXXX de la machine virtuelle YYYY" (french)
Hard disk 'XXXX.vdi' has more than one child hard disk (2).

In the snapshot manager, there were only two snapshots linked to my virtual machine.
I could delete the newest one, but I was not able to delete the oldest one/root snapshot.

To resolve this issue, I went to the "File > Virtual Media Manager" menu, then the [Hard Disks] tab and I've expanded the tree under my virtual machine.
I've deleted one snapshot that was not linked to any virtual machine, or snapshot.
After what I was able to delete my oldest/root snapshot