While I was trying installation of VirtualBox guest additions in Ubuntu 12.10 (Quantal Quetzal), I encountered the below error.
.... Warning: unknown version of the X Window System installed. Not installing X Window System drivers. ....
The effect of this error is that the VM display does not resize automatically when I choose full screen and limits the display resolution to 1024×768 pixels.
The fix for this issue is explained at: http://askubuntu.com/questions/204098/error-building-main-guest-additions-module-while-installing-virtualbox-guest-add.
# Solution: Install the X-Windows System Drivers in the Guest. sudo apt-get install virtualbox-guest-x11
Note that this does not alter the message displayed while installing VBox Guest Additions, instead fixes the full screen display issue.