If VirtualBox is trying to force a 'umount', then the Guest Additions ISO image is presumably already mounted, and you are trying to unmount it.
In a terminal, type 'mount', and you should see something along the lines of '/dev/hdc on /mnt/cdrom type iso9660 (ro)'. If you don't see something like that, then type the following to install the VirtualBox Guest Additions:Code:mkdir /mnt/cdrom && mount /dev/cdrom3 /mnt/cdrom && /mnt/cdrom/autorun.sh'




