When upgrading KDE to the latest version (de Kubuntu-Backports) DBUS stopped working:
qdbus org.kde.amarok /Player
qdbus: could not find a Qt installation of ''
Apparently there is a hodgepodge of dependencies now that they are porting everything to QT5, and you need to install qtchooser, or some other development package. The thing is that all the necessary ones are installed with qt-default:
apt-get install qt4-default
Be careful, it has to be the same version of dbus. If we install QT5 with DBUS 4, we get:
qdbus: could not exec '/usr/lib/x86_64-linux-gnu/qt5/bin/qdbus': No such file or directory