Comment 14 for bug 368508

@Bob:
First, to fix this error type:-
sudo sed -ie "s/^\s*main.*$//g" /etc/apt/sources.list

It is important that the first line you type is all on one line (I think that launchpad may have cut it in half), instead type these four lines but make sure that you DONT SPLIT ANY OF THE LINES (Each time there is a new line the Terminal reads that as a new command).

# LINE 1
SRCLINE="deb http://archive.ubuntu.com/ubuntu/ jaunty-proposed restricted main multiverse universe"
# ^^^^ ALL ON ONE LINE!!! ^^^^

# LINE 2
echo "$SRCLINE" | sudo tee -a /etc/apt/sources.list

# LINE 3
sudo apt-get update

# LINE 4
sudo aptitude -t jaunty-proposed install libical0

Also my apologies, I should have anticipated this.