virtualbox.org

I installed Guest Additions a few months ago on my Linux Guest but now when I attempt to do full screen the linux window remains the same size like it used to before I installed Guest Additions. Mouse integration still works fine, but for some reason the full screen just won't work. Uninstalling / reinstalling GA has no effect. Any ideas?

This is more than likely due to a kernel mismatch with the headers and you may have a hard time getting them to match since 8.10 is not supported anymore by Ubuntu IIRC.
Try booting to a previous kernel in Ubuntu and see if screen will resize properly.

Alright. how do i go about booting into a previous kernel? I guess it's some key I have to press while Ubuntu loads?

Oh sorry: I'm on 9.10, not 8.10. My bad.

You might want to keep this link handy https://help.ubuntu.com/
8.10 you pressed the esc key at boot IICR starting with 9.04 or 9.10 you hold down the left shift key.