Comment 2 for bug 1438745

I had already successfully upgraded mu Ubuntu 14.10 to run the new 4.0 kernel (rebooted nicely):
~$ uname -r
4.0.0-040000-generic

So naturally, I decided to perform an early upgrade to Ubuntu 15.04:
sudo do-release-upgrade -d

I had a few config files that I copied to prevent losing my settings while letting the defaults be installed with the upgrade:
~$ sudo cp /etc/rkhunter.conf /etc/rkhunter.conf.oldery
~$ sudo cp /etc/default/netatalk /etc/default/netatalk.oldery
~$ sudo cp /etc/netatalk/AppleVolumes.default /etc/netatalk/AppleVolumes.default.oldery

When it got stuck (looping with this problem: bug/1438745).
(primary window kept trying and failing to configure clamav-daemon with some sort of error on line 626 unable to find or create something because nonexistent...)
Anywhoo, I was able to open a second terminal window. I used the new terminal window to do a few commands to try to manually run dpkg clamav-daemon (but this failed with same error).
Then the second window crashed along with dock and only window still active was the first one.
So I entered x (instead of r to recover) and was supprised to get CLI prompt.

So I decided to use apt-get to purge the clamav-daemon package and any associated config files:
sudo apt-get -fV purge clamav-daemon

And Since the above recommended auto-removing clamdscan, I followed with:
sudo apt-get -fV purge clamdscan

Once that was done, I tried to install them fresh:
sudo apt-get -fV install clamav-daemon clamdscan

And it worked with no errors!!
But it did suggest that I install a package named daemon, so I did:
sudo apt-get -fV install daemon

And that worked with no errors!!

So I ran update and upgrade:
sudo apt-get update
sudo apt-get upgrade
they both ran clean...

So then I rebooted:
sudo shutdown -r

And it booted up nicely into 15.04

And it was still running with the new linux kernel: 4.0.0-040000-generic (that I had applied earlier).

I still have to restore those config file settings that were overwritten during the upgrade:

~$ uname -r
4.0.0-040000-generic

~$ sudo cp /etc/rkhunter.conf /etc/rkhunter.conf.oldery

~$ sudo cp /etc/default/netatalk /etc/default/netatalk.oldery

~$ sudo cp /etc/netatalk/AppleVolumes.default /etc/netatalk/AppleVolumes.default.oldery