If you upgrade ubuntu to 9.04, and you cannot open compiz and can not install virtualbox-2.2. Moreover, you cannot activate in NVIDIA accelerated graphics driver ( when I am writting is version 880 ) in "Hardware Drivers". The machine told you that the version is not match. When you use "uname -r" in terminal, insteading of getting "2.6.28-11-generic", that is a correct version, you got "2.6.27-11-generic" that is an older version. If you have the problem, I mentioned above you may face a problem like me, and here is the solution. The problem is very simple. When you were upgrading your machine, ubuntu ask you to overwrite menu.lst but you did not do so. Therefore, in /boot/grub/menu.lst, you still boot from 2.6.27.11-generic that is used by ubuntu 8.10. Be careful, when you are playing with "menu.lst". You may backup your "menu.lst" by executing, $ sudo cp /boot/grub/menu.lst /boot/grub/menu.lst.bak Now you can edit menu.lst....