This happens to me, too, server installation is currently broken in some settings. This appears to be a bug or a race in the installer logic, as running the apt-get command by hand in a chroot succeeded. So apparently there is not really an error during the underlying package installation, just the installer got confused.
As a workaround I have installed 12.04 server (which installed just fine), and then upgraded to 14.04. Not pretty, but at least that worked.
This happens to me, too, server installation is currently broken in some settings. This appears to be a bug or a race in the installer logic, as running the apt-get command by hand in a chroot succeeded. So apparently there is not really an error during the underlying package installation, just the installer got confused.
As a workaround I have installed 12.04 server (which installed just fine), and then upgraded to 14.04. Not pretty, but at least that worked.