I just had the same issue when upgrading from the official KDE 4.2.2 packages from Kubuntu to the 4.2.3 packages from
deb http://ppa.launchpad.net/kubuntu-ppa/ppa/ubuntu jaunty main
The command
sudo dpkg -i --force-overwrite /var/cache/apt/archives/kdebase-runtime_4%3a4.2.3-0ubuntu1~jaunty1~ppa1_i386.deb
fixed the problem for me.
I just had the same issue when upgrading from the official KDE 4.2.2 packages from Kubuntu to the 4.2.3 packages from
deb http:// ppa.launchpad. net/kubuntu- ppa/ppa/ ubuntu jaunty main
The command
sudo dpkg -i --force-overwrite /var/cache/ apt/archives/ kdebase- runtime_ 4%3a4.2. 3-0ubuntu1~ jaunty1~ ppa1_i386. deb
fixed the problem for me.