Jut tried to install Ubutu 12.04 on my pc that I had uninstalled Windows and formatted the drive prior to installing Ubutu. Just about all the way through to the end of the installation I got a message stating "Installer has encountered an unrecoverable error and will now start a desktop session for you to .........". Cant remember the rest sorry!
The OS seems to run ok from that point once the desktop is loaded from the cd but system will not boot properly without having the Ubutu installation cd in the drive. Then of course it tries again to install.
I went through the process again telling it to erase Ubutu and reinstall Ubutu with the seme error message at the end.