Comment 3 for bug 336861

I am experiencing this as well, on two separate systems. They are both systems that were originally running standard Ubuntu, but were then switched over to Kubuntu by installing kubuntu-desktop and removing various Gnome-related packages (it's very possible that there are some remaining Gnome packages on each system - perhaps that is what's causing the problem). One system is 32-bit (home-built system with MSI motherboard, Athlon-XP-2000), and the other is AMD64 (HP Pavilion dv9010us laptop, AMD Turion X2 1.6 ghz). Both systems have Nvidia graphics cards and are running the non-free drivers.

This happens with a variety of programs: firefox, thunderbird, VMWare Workstation 6.5, and others. It seems to mostly be GTK apps that are problematic. Also, plasma freezes up at the same time - the K-menu button is unresponsive (including no mouseover effects); this lasts for a couple of minutes, when everything un-freezes, including responding to mouse-clicks that occurred while it was frozen. I'm not sure if the plasma freezes are related, but they seem to happen at the same time.

Running the programs outside of KDE (I'm currently using a very bare-bones X configuration running twm) works fine.

Attached is my .xsession-errors file as well. Note that I executed "/etc/init.d/kdm stop" to shut-down the session (which had become basically unresponsive), so that might explain some of the error messages at the very end.