So today I tried to swap some desktop packages and got not very helpful:
tasksel: aptitude failed (100)
Common solution if you google it is to run:
and fix whatever errors, if you get one. I guess most common would be missing GPG keys for some of repositories used. Another one would be to run:
apt-get -f install
to fix whatever broken packages are.
But in my case none of these helped. I found real reason why tasksel was failing by running it in test mode: