Unable to mount the CD/DVD image on the machine Sandbox

The trick is to

1. shut down the guest OS
2. in the VM manager, right-click the relevant VM and select 'settings'
3. in the Storage tab, select the cd drive w/ the guest additions in it
4. in the attributes section click the little CD symbol and select 'remove disk...'

Then, after starting the VM the guest additions should be mountable again. hth

http://askubuntu.com/questions/321589/unable-to-mount-the-cd-dvd-image-on-the-machine-sandbox

Unable to mount the CD/DVD image on the machine Sandbox

I struggled with this for about 2 hours on a Windows 7 host running Ubuntu 13.10 Server guest. In the end, I just copied over the VBoxGuestAdditions.iso to the guest (using WinSCP), mounted it, and then ran VBoxLinuxAdditions.run from the guest.

I stuck with the same problem.