virtualbox.org

virtualbox-error
failed to open the cd/dvd image
/root/...iso
Callee RC:NS_ERROR_FAILURE(0x80004005)

take a look here: http://www.virtualbox.org/ticket/3319

"Had to shut down all virtual machines and wait for VBoxSVC to shutdown. Once machine was started then everything started working. Looks like the COM server got all screwy "

I don't understand

I'd say that it's similar, or the same, as my own bug report here: http://www.virtualbox.org/ticket/3202
A remount of an ISO doesn't work for a set time, it isn't released properly. The VM says it's detached, but the Virtual Media Manager doesn't.