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!
Look on my works, ye Mighty, and despair! 
Hello, thanks for your informations…but I have a problem with the same configuration (VB 4.1.2, ubuntu 11.10) : I cannot find by which way I can install the add ons !! The usual menu (Devices -> Install guest add-ons) have diseapeared and even if I have found the add_ons iso (in the folder you give here), I do not know how to install it on my Vbox.
Could you help?
thanks a lot !
If you go to Devices -> CD/DVD Devices -> Choose a virtual CD/DVD disk file… can you mount the iso manually?
Thanks for that!
LoL
Thanks a klot works perfect
Man… What I need!!
Thanks a lot!!!
Thks a lot. Helped a lot!