I thought I should share this one. Easier than I thought, but distracted me for a while.

I use Kubuntu 9.04 "Jaunty Jackalope" (just upgraded from Intrepid).

While troubleshooting something nastier, I found in ~/.xsession-errors several instances of the error message

QGtkStyle cannot be used together with the GTK_Qt engine

I noticed it appeared after launching a GUI program, like for example:

kdeinit4: preparing to launch /usr/bin/systemsettings ...or
kdeinit4: preparing to launch /usr/bin/konqueror

It seemed that it had to do with the visual style. It did. I had recently made some cosmetic changes to KDE. In fact, the offended action was: I had selected a different "Widget style" in "System Settings" -> "Appearance" -> "Style" the style... GTK+ .. DOH!

After changing it to "Oxygen" (any other more "QT ish" would do), the message did not appear again.

An easy one, folks, just to cheer me up while I have been fighting a really tough one... (I hold the story for another time) ;-)

Ocumo