If while downloading the packages, tasksel unexpectedly exits with an error – tasksel: aptitude failed (100), do not despair. It is because the package database of your Ubuntu installation is old. Doing a sudo apt-get update will resolve the error and tasksel will be able to continue where it left off.
I tried this and it worked:
Problems Encountered And Their Solution
If while downloading the packages, tasksel unexpectedly exits with an error – tasksel: aptitude failed (100), do not despair. It is because the package database of your Ubuntu installation is old. Doing a sudo apt-get update will resolve the error and tasksel will be able to continue where it left off.
Ref: http:// linuxandfriends .com/2009/ 12/09/how- to-install- lamp-server- in-ubuntu- linux/.