Comment 2 for bug 66514

Here's my first attempt to fix it:

duncan@ubuntu:~$ sudo -s
Password:
root@ubuntu:~# apt-get install ubuntu-desktop
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.

Since you only requested a single operation it is extremely likely that
the package is simply not installable and a bug report against
that package should be filed.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
  ubuntu-desktop: Depends: xorg but it is not going to be installed
E: Broken packages
root@ubuntu:~# apt-get install xorg
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.

Since you only requested a single operation it is extremely likely that
the package is simply not installable and a bug report against
that package should be filed.
The following information may help to resolve the situation:

The following packages have unmet dependencies:
  xorg: Depends: libgl1-mesa-dri but it is not going to be installed
E: Broken packages
root@ubuntu:~# apt-get install libg11-mesa-dri
Reading package lists... Done
Building dependency tree
Reading state information... Done
E: Couldn't find package libg11-mesa-dri
root@ubuntu:~#