Comment 10 for bug 571743

I found an hack, if you doesn't want to uninstall and perhaps loose settings:
Its dirty, but it worked.

I did that in the shell with sudo do-release-upgrade
I attached strace till the error cames out then and then I stopped it.
I checked the log file from strace and found out, that
a file was created: /tmp/<folder_with_random_chars>/removal_blacklist.cfg

So I let it restore to the old state, cleared the tmp folder,
restarted the tool and quick removed the *untu-dektop entries in the file removal_blacklist.cfg (there is then only one folder with random charas only in the tem dir), and saved.
i recommend vim because you can go quick in then type "d6d" (i think there are 6 lines) in command mode type :x and its saved.
I needed two runs, so you have to be quite fast till the updater reads the file.