When doing the guest additions install using CLI, I told the system to install anyway at the existing additions question. Everything works great.
+1. You can either load Synaptic, do a search for VirtualBox, and uninstall the guest additions package. Or you can do as rick0612 says. Use the CLI method to install, and after the message, install the new guest additions. Both methods should give you the same result.
One way to install from the command line is to su to root, and then make sure you are in the VBOXADDITIONS
"CD" and run the command:sh V*run
Let it do it's thing - reboot and you should be good to go.
Note - in VBox if you use the Devices > Install Guest Additions
option you should ( in KDE at least ) be prompted what you want to do - you can choose Dolphin and then use F4 to split the window and open the terminal in the bottom half; if you use this method, su to root and then press F4 twice
to bring you back to the CD location..........