Application that crashed: kwin
Version of the application: 4.3.2 (KDE 4.3.2)
KDE Version: 4.3.2 (KDE 4.3.2)
Qt Version: 4.5.2
Operating System: Linux 2.6.31-20-generic i686
Distribution: Ubuntu 9.10

What I was doing when the application crashed:
KWin crashed upon window switching using Alt+Tab and composting enabled.

 -- Backtrace:
Application: KWin (kwin), signal: Segmentation fault
[KCrash Handler]
#6  WindowPaintData (this=0xbf802270, w=0x1) at ../../../kwin/lib/kwineffects.cpp:76
#7  0x02e5e917 in KWin::CoverSwitchEffect::paintFrontWindow (this=0x9a317d8, frontWindow=0x1, width=1024, leftWindows=2, rightWindows=2, reflectedWindow=false)
    at ../../../kwin/effects/coverswitch/coverswitch.cpp:801
#8  0x02e5fc28 in KWin::CoverSwitchEffect::paintScene (this=0x9a317d8, frontWindow=0x1, leftWindows=..., rightWindows=..., reflectedWindows=false)
    at ../../../kwin/effects/coverswitch/coverswitch.cpp:436
#9  0x02e661f3 in KWin::CoverSwitchEffect::paintScreen (this=0x9a317d8, mask=32, region=..., data=...) at ../../../kwin/effects/coverswitch/coverswitch.cpp:308
#10 0x00d99a90 in KWin::EffectsHandlerImpl::paintScreen (this=0x99ad420, mask=32, region=..., data=...) at ../../kwin/effects.cpp:122
#11 0x00138c66 in KWin::Effect::paintScreen (this=0x9a78558, mask=32, region=..., data=...) at ../../../kwin/lib/kwineffects.cpp:206
#12 0x00d99a90 in KWin::EffectsHandlerImpl::paintScreen (this=0x99ad420, mask=32, region=..., data=...) at ../../kwin/effects.cpp:122
#13 0x00138c66 in KWin::Effect::paintScreen (this=0x9a964a8, mask=32, region=..., data=...) at ../../../kwin/lib/kwineffects.cpp:206
#14 0x00d99a90 in KWin::EffectsHandlerImpl::paintScreen (this=0x99ad420, mask=32, region=..., data=...) at ../../kwin/effects.cpp:122
#15 0x02e5cdd3 in KWin::ZoomEffect::paintScreen (this=0x9a8a4c0, mask=32, region=..., data=...) at ../../../kwin/effects/zoom/zoom.cpp:73
#16 0x00d99a90 in KWin::EffectsHandlerImpl::paintScreen (this=0x99ad420, mask=32, region=..., data=...) at ../../kwin/effects.cpp:122
#17 0x00d82604 in KWin::Scene::paintScreen (this=0x99b18f0, mask=0xbf802858, region=0xbf802918) at ../../kwin/scene.cpp:134
#18 0x00d92213 in KWin::SceneOpenGL::paint (this=0x99b18f0, damage=..., toplevels=...) at ../../kwin/scene_opengl.cpp:746
#19 0x00d7dcd1 in KWin::Workspace::performCompositing (this=0x99aa1f0) at ../../kwin/composite.cpp:420
#20 0x00d0c79a in KWin::Workspace::qt_metacall (this=0x99aa1f0, _c=QMetaObject::InvokeMetaMethod, _id=153, _a=0xbf802a0c) at ./workspace.moc:473
#21 0x09786263 in QMetaObject::activate (sender=0x99aa454, from_signal_index=4, to_signal_index=4, argv=0x0) at kernel/qobject.cpp:3113
#22 0x09786ec2 in QMetaObject::activate (sender=0x99aa454, m=0x9861904, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3187
#23 0x097c0667 in QTimer::timeout (this=0x99aa454) at .moc/release-shared/moc_qtimer.cpp:128
#24 0x0978b9ae in QTimer::timerEvent (this=0x99aa454, e=0xbf802ec0) at kernel/qtimer.cpp:261
#25 0x097803bf in QObject::event (this=0x99aa454, e=0xbf802ec0) at kernel/qobject.cpp:1075
#26 0x08dadf54 in QApplicationPrivate::notify_helper (this=0x98eab50, receiver=0x99aa454, e=0xbf802ec0) at kernel/qapplication.cpp:4056
#27 0x08db567c in QApplication::notify (this=0xbf803238, receiver=0x99aa454, e=0xbf802ec0) at kernel/qapplication.cpp:3603
#28 0x00597bfa in KApplication::notify (this=0xbf803238, receiver=0x99aa454, event=0xbf802ec0) at ../../kdeui/kernel/kapplication.cpp:302
#29 0x00d2246f in KWin::Application::notify (this=0xbf803238, o=0x99aa454, e=0xbf802ec0) at ../../kwin/main.cpp:366
#30 0x097706cb in QCoreApplication::notifyInternal (this=0xbf803238, receiver=0x99aa454, event=0xbf802ec0) at kernel/qcoreapplication.cpp:610
#31 0x0979d7ce in QCoreApplication::sendEvent (this=0x98edd34) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#32 QTimerInfoList::activateTimers (this=0x98edd34) at kernel/qeventdispatcher_unix.cpp:572
#33 0x0979b0e0 in timerSourceDispatch (source=0x98edd00) at kernel/qeventdispatcher_glib.cpp:165
#34 0x07da2e88 in g_main_context_dispatch () from /lib/libglib-2.0.so.0
#35 0x07da6730 in ?? () from /lib/libglib-2.0.so.0
#36 0x07da6863 in g_main_context_iteration () from /lib/libglib-2.0.so.0
#37 0x0979b02c in QEventDispatcherGlib::processEvents (this=0x98d4b68, flags=...) at kernel/qeventdispatcher_glib.cpp:327
#38 0x08e4ebe5 in QGuiEventDispatcherGlib::processEvents (this=0x98d4b68, flags=...) at kernel/qguieventdispatcher_glib.cpp:202
#39 0x0976ec79 in QEventLoop::processEvents (this=0xbf803184, flags=) at kernel/qeventloop.cpp:149
#40 0x0976f0ca in QEventLoop::exec (this=0xbf803184, flags=...) at kernel/qeventloop.cpp:201
#41 0x0977153f in QCoreApplication::exec () at kernel/qcoreapplication.cpp:888
#42 0x08daddd7 in QApplication::exec () at kernel/qapplication.cpp:3525
#43 0x00d25034 in kdemain (argc=3, argv=0xbf803434) at ../../kwin/main.cpp:522
#44 0x080485cb in main (argc=3, argv=0xbf803434) at kwin_dummy.cpp:3

Reported using DrKonqi