Comment 11 for bug 16337

(In reply to comment #8)
> Does someone found a solution for this ?

Yep :)

1) apt-remove --purge kubuntu-default-settings (watch for its dependencies, you'll reinstall them
later)

2) rm -rf /etc/qt3

3) apt-get install kubuntu-default-settings (and every package which was removed)

My guessing is that having /etc/qt3/.qt_plugins_3.3rc.lock and /etc/qt3/.qtrc.lock during an
upgrade causes this (I don't know why, sorry)