I’m not sure why this is but Ubuntu 8.04 LTS will not install on VirtualBox. I even downgraded VirtualBox to the version 2 series, and it still would not install. (What I thought was weird about these downgrades is that I asked it to complete the installation in a different folder SUN/Virtualbox-3.06. It overwrote SUN/Virtualbox folder and renamed it to VirtualBox-2.24)
Firstly Ubuntu 8.04 would not install at all. I had to set in the virtual machine under VirtualBox tabs
System-> Enable APIC and I/O APIC
So the next hurdle was an error message about a kernel not being able to be built and the installation would not complete.
"no installable kernel was found in the defined APT sources."
At this point press Alt+F2 to switch to console. Press Enter to activate console and then:
chroot /target apt-get install linux-generic
Once the kernel installation is complete (this takes about 10 minutes or so) type the following
Press Alt+F1 to return to the installer and then answer “Yes” to the “Continue without installing a kernel?”
The installation will take about another 30 minutes or so and then your system should be up and running.