Getting an error wrong fs type, bad option, bad superblock on UbuntuShared
Solution 1:
Apparently there is a bad symlink. I had the exact same problem and this fixed it. Good luck.
sudo ln -s /opt/VBoxGuestAdditions-4.3.10/lib/VBoxGuestAdditions /usr/lib/VBoxGuestAdditions
Found solution here: https://forums.virtualbox.org/viewtopic.php?f=3&t=60921