Application that crashed: kwin
Version of the application: 4.3.1 (KDE 4.3.1)
KDE Version: 4.3.1 (KDE 4.3.1)
Qt Version: 4.5.2
Operating System: Linux 2.6.28-15-generic x86_64
Distribution: Ubuntu 9.04

What I was doing when the application crashed:
I added the activity bar widget, after that plasma didn't react on any user input. about 5 seconds later it crashed.

 -- Backtrace:
Application: KWin (kwin), signal: Segmentation fault
[KCrash Handler]
#5  0x0000000001a9dca0 in ?? ()
#6  0x00007f4f13610e37 in WindowPaintData (this=0x7fff1bf379c0, w=0x1d43330) at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:76
#7  0x00007f4f045b2a87 in KWin::BoxSwitchEffect::paintWindowThumbnail (this=0x1aa87d0, w=0x1d43330) at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/boxswitch/boxswitch.cpp:747
#8  0x00007f4f045b471f in KWin::BoxSwitchEffect::paintScreen (this=0x1aa87d0, mask=0, region={d = 0x0, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, 
    data=<value optimized out>) at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/boxswitch/boxswitch.cpp:157
#9  0x00007f4f13aed137 in KWin::EffectsHandlerImpl::paintScreen (this=0x19a0e70, mask=0, region=
        {d = 0x7fff1bf37e80, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#10 0x00007f4f045ff397 in KWin::CubeEffect::paintScreen (this=0x1aaa380, mask=0, region=
        {d = 0x7fff1bf38000, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/cube/cube.cpp:669
#11 0x00007f4f13aed137 in KWin::EffectsHandlerImpl::paintScreen (this=0x19a0e70, mask=0, region=
        {d = 0x7fff1bf38050, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#12 0x00007f4f1360e660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=0, region=<value optimized out>, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#13 0x00007f4f13aed137 in KWin::EffectsHandlerImpl::paintScreen (this=0x19a0e70, mask=0, region=
        {d = 0x7fff1bf38260, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#14 0x00007f4f04606aa4 in KWin::CubeSlideEffect::paintScreen (this=0x1a69640, mask=0, region=
        {d = 0x7fff1bf38310, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/cube/cubeslide.cpp:109
#15 0x00007f4f13aed137 in KWin::EffectsHandlerImpl::paintScreen (this=0x19a0e70, mask=0, region=
        {d = 0x7fff1bf38360, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#16 0x00007f4f1360e660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=0, region=<value optimized out>, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#17 0x00007f4f13aed137 in KWin::EffectsHandlerImpl::paintScreen (this=0x19a0e70, mask=0, region=
        {d = 0x7fff1bf38410, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#18 0x00007f4f1360e660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=0, region=<value optimized out>, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#19 0x00007f4f13aed137 in KWin::EffectsHandlerImpl::paintScreen (this=0x19a0e70, mask=0, region=
        {d = 0x7fff1bf38560, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff1bf384e0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#20 0x00007f4f13ad873c in KWin::Scene::paintScreen (this=0x1910770, mask=0x7fff1bf3866c, region=0x7fff1bf38780) at /build/buildd/kdebase-workspace-4.3.1/kwin/scene.cpp:134
#21 0x00007f4f13ae72ef in KWin::SceneOpenGL::paint (this=0x1910770, damage={d = 0x7fff1bf38780, static shared_empty = {ref = {_q_value = 607}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, 
    toplevels=<value optimized out>) at /build/buildd/kdebase-workspace-4.3.1/kwin/scene_opengl.cpp:746
#22 0x00007f4f13ad38e2 in KWin::Workspace::performCompositing (this=0x192c890) at /build/buildd/kdebase-workspace-4.3.1/kwin/composite.cpp:420
#23 0x00007f4f13a6ef5a in KWin::Workspace::qt_metacall (this=0x192c890, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fff1bf38910)
    at /build/buildd/kdebase-workspace-4.3.1/obj-x86_64-linux-gnu/kwin/workspace.moc:473
#24 0x00007f4f111aaea2 in QMetaObject::activate (sender=0x192ccb8, from_signal_index=<value optimized out>, to_signal_index=4, argv=0x11) at kernel/qobject.cpp:3113
#25 0x00007f4f111a5263 in QObject::event (this=0x192ccb8, e=0x1d43330) at kernel/qobject.cpp:1075
#26 0x00007f4f1189ef4d in QApplicationPrivate::notify_helper (this=0x170bf40, receiver=0x192ccb8, e=0x7fff1bf38fc0) at kernel/qapplication.cpp:4056
#27 0x00007f4f118a718a in QApplication::notify (this=0x7fff1bf39330, receiver=0x192ccb8, e=0x7fff1bf38fc0) at kernel/qapplication.cpp:4021
#28 0x00007f4f12de0deb in KApplication::notify (this=0x7fff1bf39330, receiver=0x192ccb8, event=0x7fff1bf38fc0) at /build/buildd/kde4libs-4.3.1/kdeui/kernel/kapplication.cpp:302
#29 0x00007f4f111956ac in QCoreApplication::notifyInternal (this=0x7fff1bf39330, receiver=0x192ccb8, event=0x7fff1bf38fc0) at kernel/qcoreapplication.cpp:610
#30 0x00007f4f111c2516 in QTimerInfoList::activateTimers (this=0x170fc60) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#31 0x00007f4f111beb2d in timerSourceDispatch (source=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:165
#32 0x00007f4f0a49b20a in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#33 0x00007f4f0a49e8e0 in ?? () from /usr/lib/libglib-2.0.so.0
#34 0x00007f4f0a49ea7c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#35 0x00007f4f111bea8f in QEventDispatcherGlib::processEvents (this=0x16f2fb0, flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:327
#36 0x00007f4f11937bdf in QGuiEventDispatcherGlib::processEvents (this=0x1d43330, flags=<value optimized out>) at kernel/qguieventdispatcher_glib.cpp:202
#37 0x00007f4f11193f42 in QEventLoop::processEvents (this=<value optimized out>, flags={i = 468947504}) at kernel/qeventloop.cpp:149
#38 0x00007f4f11194314 in QEventLoop::exec (this=0x7fff1bf39270, flags={i = 468947584}) at kernel/qeventloop.cpp:201
#39 0x00007f4f111965e4 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
#40 0x00007f4f13a87278 in kdemain (argc=3, argv=0x7fff1bf39818) at /build/buildd/kdebase-workspace-4.3.1/kwin/main.cpp:522
#41 0x00007f4f0e5e05a6 in __libc_start_main (main=0x4008c0 <main>, argc=3, ubp_av=0x7fff1bf39818, init=0x4008f0 <__libc_csu_init>, fini=<value optimized out>, rtld_fini=<value optimized out>, 
    stack_end=0x7fff1bf39808) at libc-start.c:220
#42 0x00000000004007f9 in _start () at ../sysdeps/x86_64/elf/start.S:113

Reported using DrKonqi