It's best to use miske's answer.
If you really want to use natecarlson's repository, the instructions just below can do any of the following:
apt-get update gives a 404 error after add-apt-repositoryapt-get update gives a NO_PUBKEY error after manually adding it to /etc/apt/sources.listOpen a terminal and run the following:
sudo -i
Enter your password if necessary, then paste the following into the terminal:
export GOOD_RELEASE='precise'
export BAD_RELEASE="`lsb_release -cs`"
cd /etc/apt
sed -i '/natecarlson\/maven3/d' sources.list
cd sources.list.d
rm -f natecarlson-maven3-*.list*
apt-add-repository -y ppa:natecarlson/maven3
mv natecarlson-maven3-${BAD_RELEASE}.list natecarlson-maven3-${GOOD_RELEASE}.list
sed -i "s/${BAD_RELEASE}/${GOOD_RELEASE}/" natecarlson-maven3-${GOOD_RELEASE}.list
apt-get update
exit
echo Done!
If you installed natecarlson's repository (either using add-apt-repository or manually added to /etc/apt/sources.list) and you don't want it anymore, open a terminal and run the following:
sudo -i
Enter your password if necessary, then paste the following into the terminal:
cd /etc/apt
sed -i '/natecarlson\/maven3/d' sources.list
cd sources.list.d
rm -f natecarlson-maven3-*.list*
apt-get update
exit
echo Done!