I’ve been having some trouble copying files from my host fileshare (\\vboxsvr), and the internets recommended re-installing the guest additions. Unfortunately, trying to download the guest additions iso resulted in the error below:
Some frantic searching of the VBox forums offered a solution: download the guest additions for the previous version (4.1.0), and put them in the location VBox expects to find them (either /usr/share/virtualbox/VBoxGuestAdditions.iso or /usr/lib/virtualbox/additions/VBoxGuestAdditions.iso).
sudo mv VBoxGuestAdditions_4.1.0.iso /usr/share/virtualbox/VBoxGuestAdditions.iso
And now I can copy files without any problems, hurray!