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:
Turned compositing back on alt tab and then kwin crash, using ATI 9.7 or 9.8 fglrx driver and compositing causes problems with this driver.

 -- Backtrace:
Application: KWin (kwin), signal: Segmentation fault
[KCrash Handler]
#5  KWin::FlipSwitchEffect::paintScreen (this=0x1ead040, mask=<value optimized out>, region=
        {d = 0x7fff97763f90, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=<value optimized out>)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/flipswitch/flipswitch.cpp:199
#6  0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764140, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#7  0x00007f2e8171eaa4 in KWin::CubeSlideEffect::paintScreen (this=0x1bc8050, mask=32, region=
        {d = 0x7fff977641f0, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/cube/cubeslide.cpp:109
#8  0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff977643b0, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#9  0x00007f2e816ce9b4 in KWin::DesktopGridEffect::paintScreen (this=0x1bc5bb0, mask=32, region=
        {d = 0x7fff97764420, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/desktopgrid/desktopgrid.cpp:140
#10 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764540, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#11 0x00007f2e81717397 in KWin::CubeEffect::paintScreen (this=0x1eac9b0, mask=32, region=
        {d = 0x7fff977646c0, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/cube/cube.cpp:669
#12 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764710, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#13 0x00007f2e8ee3b660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=32, region=<value optimized out>, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#14 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff977647c0, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#15 0x00007f2e8ee3b660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=32, region=<value optimized out>, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#16 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764870, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#17 0x00007f2e8ee3b660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=32, region=<value optimized out>, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#18 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764920, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#19 0x00007f2e8ee3b660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=32, region=<value optimized out>, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#20 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff977649d0, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#21 0x00007f2e8ee3b660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=32, region=<value optimized out>, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#22 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764a90, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#23 0x00007f2e81706c65 in KWin::ZoomEffect::paintScreen (this=<value optimized out>, mask=32, region=
        {d = 0x7fff97764b00, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/zoom/zoom.cpp:73
#24 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764b50, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#25 0x00007f2e8ee3b660 in KWin::Effect::paintScreen (this=<value optimized out>, mask=32, region=<value optimized out>, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/lib/kwineffects.cpp:206
#26 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764cd0, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#27 0x00007f2e817046e4 in KWin::ThumbnailAsideEffect::paintScreen (this=0x1a1c910, mask=32, region=
        {d = 0x7fff97764d40, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects/thumbnailaside/thumbnailaside.cpp:56
#28 0x00007f2e8f31a137 in KWin::EffectsHandlerImpl::paintScreen (this=0x1994b90, mask=32, region=
        {d = 0x7fff97764e30, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, data=@0x7fff97764db0)
    at /build/buildd/kdebase-workspace-4.3.1/kwin/effects.cpp:122
#29 0x00007f2e8f30573c in KWin::Scene::paintScreen (this=0x1945d70, mask=0x7fff97764f3c, region=0x7fff97765050) at /build/buildd/kdebase-workspace-4.3.1/kwin/scene.cpp:134
#30 0x00007f2e8f3142ef in KWin::SceneOpenGL::paint (this=0x1945d70, damage={d = 0x7fff97765050, static shared_empty = {ref = {_q_value = 437}, rgn = 0x0, xrectangles = 0x0, qt_rgn = 0x0}}, 
    toplevels=<value optimized out>) at /build/buildd/kdebase-workspace-4.3.1/kwin/scene_opengl.cpp:746
#31 0x00007f2e8f3008e2 in KWin::Workspace::performCompositing (this=0x18966a0) at /build/buildd/kdebase-workspace-4.3.1/kwin/composite.cpp:420
#32 0x00007f2e8f29bf5a in KWin::Workspace::qt_metacall (this=0x18966a0, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fff977651e0)
    at /build/buildd/kdebase-workspace-4.3.1/obj-x86_64-linux-gnu/kwin/workspace.moc:473
#33 0x00007f2e8c9d7ea2 in QMetaObject::activate (sender=0x1896ac8, from_signal_index=<value optimized out>, to_signal_index=4, argv=0x1) at kernel/qobject.cpp:3113
#34 0x00007f2e8c9d2263 in QObject::event (this=0x1896ac8, e=0x18f8e30) at kernel/qobject.cpp:1075
#35 0x00007f2e8d0cbf4d in QApplicationPrivate::notify_helper (this=0x178f940, receiver=0x1896ac8, e=0x7fff97765890) at kernel/qapplication.cpp:4056
#36 0x00007f2e8d0d418a in QApplication::notify (this=0x7fff97765c00, receiver=0x1896ac8, e=0x7fff97765890) at kernel/qapplication.cpp:4021
#37 0x00007f2e8e60ddeb in KApplication::notify (this=0x7fff97765c00, receiver=0x1896ac8, event=0x7fff97765890) at /build/buildd/kde4libs-4.3.1/kdeui/kernel/kapplication.cpp:302
#38 0x00007f2e8c9c26ac in QCoreApplication::notifyInternal (this=0x7fff97765c00, receiver=0x1896ac8, event=0x7fff97765890) at kernel/qcoreapplication.cpp:610
#39 0x00007f2e8c9ef516 in QTimerInfoList::activateTimers (this=0x1793640) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#40 0x00007f2e8c9ebb2d in timerSourceDispatch (source=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:165
#41 0x00007f2e85eba20a in IA__g_main_context_dispatch (context=0x1792520) at /build/buildd/glib2.0-2.20.1/glib/gmain.c:1814
#42 0x00007f2e85ebd8e0 in g_main_context_iterate (context=0x1792520, block=1, dispatch=1, self=<value optimized out>) at /build/buildd/glib2.0-2.20.1/glib/gmain.c:2448
#43 0x00007f2e85ebda7c in IA__g_main_context_iteration (context=0x1792520, may_block=1) at /build/buildd/glib2.0-2.20.1/glib/gmain.c:2511
#44 0x00007f2e8c9eba8f in QEventDispatcherGlib::processEvents (this=0x1776940, flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:327
#45 0x00007f2e8d164bdf in QGuiEventDispatcherGlib::processEvents (this=0x1f3f350, flags=<value optimized out>) at kernel/qguieventdispatcher_glib.cpp:202
#46 0x00007f2e8c9c0f42 in QEventLoop::processEvents (this=<value optimized out>, flags={i = -1753851136}) at kernel/qeventloop.cpp:149
#47 0x00007f2e8c9c1314 in QEventLoop::exec (this=0x7fff97765b40, flags={i = -1753851056}) at kernel/qeventloop.cpp:201
#48 0x00007f2e8c9c35e4 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
#49 0x00007f2e8f2b4278 in kdemain (argc=3, argv=0x7fff977660e8) at /build/buildd/kdebase-workspace-4.3.1/kwin/main.cpp:522
#50 0x00007f2e89fff5a6 in __libc_start_main (main=0x4008c0 <main>, argc=3, ubp_av=0x7fff977660e8, init=0x4008f0 <__libc_csu_init>, fini=<value optimized out>, rtld_fini=<value optimized out>, 
    stack_end=0x7fff977660d8) at libc-start.c:220
#51 0x00000000004007f9 in _start () at ../sysdeps/x86_64/elf/start.S:113

Reported using DrKonqi