Why does "tasksel" give an "aptitude failed" error?

This is a long outstanding bug.

Do

sudo apt-get update

then

sudo tasksel install lamp-server  

Oh and if this ever happens when you (re)install MySQL itself make sure to remove /var/lib/mysql.

edit: Found it on Launchpad from a report in 2007.

Nowadays you can also do

sudo apt-get install lamp-server^

The ^ is the equivalent of task select.

I know this thread isn't new and shiny and also this has already been answered but for those who encounter the issue again; I found that I received this error whilst trying to use tasksel to install whilst not having enough storage space left on my device. After removing some files and cleaning up the system of a little of junk, I tried again with success.

After clearing up I used:

apt-get -f install

As suggested by izx

After which, tasksel worked as usually expected.