A guy ("spiroo") in IRC just posted the same crash - he had a slightly more complete backtrace, though:

#0  QGraphicsLayoutItem::geometry (this=0x10) at graphicsview/qgraphicslayoutitem.cpp:663
#1  0xb6e98bbf in QGraphicsWidget::size (this=0x0) at graphicsview/qgraphicswidget.cpp:326
#2  0xb7f25aae in ?? () from /usr/lib/libkdeinit4_plasma-desktop.so
#3  0xb7d9cf9e in Plasma::Corona::initializeLayout (this=0x9b844b0, configName=@0xbfca9fb4) at /build/buildd/kde4libs-4.2.95/plasma/corona.cpp:326
#4  0xb7f41f17 in ?? () from /usr/lib/libkdeinit4_plasma-desktop.so
#5  0xb7f420c4 in ?? () from /usr/lib/libkdeinit4_plasma-desktop.so
#6  0xb7f466b0 in ?? () from /usr/lib/libkdeinit4_plasma-desktop.so
#7  0xb657fca8 in QMetaObject::activate (sender=0x9b812f8, from_signal_index=4, to_signal_index=4, argv=0x0) at kernel/qobject.cpp:3069
#8  0xb6580932 in QMetaObject::activate (sender=0x9b812f8, m=0xb665b908, local_signal_index=0, argv=0x0) at kernel/qobject.cpp:3143
#9  0xb65850a7 in QSingleShotTimer::timeout (this=0x9b812f8) at .moc/release-shared/qtimer.moc:76
#10 0xb65851cc in QSingleShotTimer::timerEvent (this=0x9b812f8) at kernel/qtimer.cpp:298
#11 0xb657a15f in QObject::event (this=0x9b812f8, e=0xbfcaa59c) at kernel/qobject.cpp:1082
#12 0xb6816e9c in QApplicationPrivate::notify_helper (this=0x9b2ccb0, receiver=0x9b812f8, e=0xbfcaa59c) at kernel/qapplication.cpp:4084
#13 0xb681f19e in QApplication::notify (this=0x9b274e0, receiver=0x9b812f8, e=0xbfcaa59c) at kernel/qapplication.cpp:3631
#14 0xb767f3dd in KApplication::notify (this=0x9b274e0, receiver=0x9b812f8, event=0xbfcaa59c) at /build/buildd/kde4libs-4.2.95/kdeui/kernel/kapplication.cpp:302
#15 0xb6569a3b in QCoreApplication::notifyInternal (this=0x9b274e0, receiver=0x9b812f8, event=0xbfcaa59c) at kernel/qcoreapplication.cpp:602
#16 0xb6598d71 in QTimerInfoList::activateTimers (this=0x9b33f74) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#17 0xb65954e0 in timerSourceDispatch (source=0x9b33f40) at kernel/qeventdispatcher_glib.cpp:164
#18 0xb4e2db88 in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#19 0xb4e310eb in ?? () from /usr/lib/libglib-2.0.so.0
#20 0xb4e31268 in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#21 0xb6595438 in QEventDispatcherGlib::processEvents (this=0x9b2c290, flags={i = -1077237992}) at kernel/qeventdispatcher_glib.cpp:323
#22 0xb68b8365 in QGuiEventDispatcherGlib::processEvents (this=0x9b2c290, flags={i = -1077237944}) at kernel/qguieventdispatcher_glib.cpp:202
#23 0xb656806a in QEventLoop::processEvents (this=0xbfcaa7c0, flags={i = -1077237880}) at kernel/qeventloop.cpp:149
#24 0xb65684aa in QEventLoop::exec (this=0xbfcaa7c0, flags={i = -1077237816}) at kernel/qeventloop.cpp:200
#25 0xb656a959 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:880
#26 0xb6816d17 in QApplication::exec () at kernel/qapplication.cpp:3553
#27 0xb7f2a510 in kdemain () from /usr/lib/libkdeinit4_plasma-desktop.so
#28 0x08048712 in _start ()

*** Bug 199211 has been marked as a duplicate of this bug. ***

What are your KDE and Qt versions (svn revision/branch) ?
If you can reproduce the crash at will, may you read http://techbase.kde.org/Development/Tutorials/Debugging/How_to_create_useful_crash_reports and post a complete backtrace here? You need debug symbols for kdebase-workspace. Thanks

KDE 4.3 RC1
Unbuntu Jaunty - Linux 2.6.28-13
Machine x64
I am installing the dbg packages now.
The KDE was instaled using this repo deb http://ppa.launchpad.net/kubuntu-ppa/backports/ubuntu jaunty main

Application that crashed: plasma-desktop
Version of the application: 0.3
KDE Version: 4.2.95 (KDE 4.2.95 (KDE 4.3 RC1))
Qt Version: 4.5.0
Operating System: Linux 2.6.28-13-generic x64
Distribution: Ubuntu 9.04


Application: Plasma Workspace (kdeinit4), signal: Segmentation fault
[KCrash Handler]
#5  QGraphicsLayoutItem::geometry (this=0x20) at graphicsview/qgraphicslayoutitem.cpp:663
#6  0x00007f3588d9c825 in QGraphicsWidget::size (this=<value optimized out>) at graphicsview/qgraphicswidget.cpp:326
#7  0x00007f357fdc4019 in DesktopCorona::loadDefaultLayout (this=0x7c6340) at /build/buildd/kdebase-workspace-4.2.95/plasma/shells/desktop/desktopcorona.cpp:234
#8  0x00007f3582ad1615 in Plasma::Corona::initializeLayout (this=0x7c6340, configName=@0x7fff93714300) at /build/buildd/kde4libs-4.2.95/plasma/corona.cpp:326
#9  0x00007f357fdddb7d in PlasmaApp::corona (this=0x71a4d0) at /build/buildd/kdebase-workspace-4.2.95/plasma/shells/desktop/plasmaapp.cpp:574
#10 0x00007f357fdddd08 in PlasmaApp::setupDesktop (this=0x71a4d0) at /build/buildd/kdebase-workspace-4.2.95/plasma/shells/desktop/plasmaapp.cpp:252
#11 0x00007f357fde1d65 in PlasmaApp::qt_metacall (this=0x71a4d0, _c=QMetaObject::InvokeMetaMethod, _id=<value optimized out>, _a=0x7fff937145a0)
    at /build/buildd/kdebase-workspace-4.2.95/obj-x86_64-linux-gnu/plasma/shells/desktop/plasmaapp.moc:115
#12 0x00007f358b2141f2 in QMetaObject::activate (sender=0x805610, from_signal_index=<value optimized out>, to_signal_index=4, argv=0x0) at kernel/qobject.cpp:3069
#13 0x00007f358b21952f in QSingleShotTimer::timerEvent (this=0x805610) at kernel/qtimer.cpp:298
#14 0x00007f358b20e4d3 in QObject::event (this=0x805610, e=0x20) at kernel/qobject.cpp:1082
#15 0x00007f358878878d in QApplicationPrivate::notify_helper (this=0x759990, receiver=0x805610, e=0x7fff93714c60) at kernel/qapplication.cpp:4084
#16 0x00007f358879097a in QApplication::notify (this=0x71a4d0, receiver=0x805610, e=0x7fff93714c60) at kernel/qapplication.cpp:4049
#17 0x00007f35898cb62b in KApplication::notify (this=0x71a4d0, receiver=0x805610, event=0x7fff93714c60) at /build/buildd/kde4libs-4.2.95/kdeui/kernel/kapplication.cpp:302
#18 0x00007f358b1fe75c in QCoreApplication::notifyInternal (this=0x71a4d0, receiver=0x805610, event=0x7fff93714c60) at kernel/qcoreapplication.cpp:602
#19 0x00007f358b22b7f6 in QTimerInfoList::activateTimers (this=0x75d0f0) at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:213
#20 0x00007f358b227f0d in timerSourceDispatch (source=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:164
#21 0x00007f35871e620a in g_main_context_dispatch () from /usr/lib/libglib-2.0.so.0
#22 0x00007f35871e98e0 in ?? () from /usr/lib/libglib-2.0.so.0
#23 0x00007f35871e9a7c in g_main_context_iteration () from /usr/lib/libglib-2.0.so.0
#24 0x00007f358b227e6f in QEventDispatcherGlib::processEvents (this=0x759630, flags=<value optimized out>) at kernel/qeventdispatcher_glib.cpp:323
#25 0x00007f3588820bef in QGuiEventDispatcherGlib::processEvents (this=0x7fff93713be0, flags=<value optimized out>) at kernel/qguieventdispatcher_glib.cpp:202
#26 0x00007f358b1fd002 in QEventLoop::processEvents (this=<value optimized out>, flags={i = -1821290800}) at kernel/qeventloop.cpp:149
#27 0x00007f358b1fd3cd in QEventLoop::exec (this=0x7fff93714f10, flags={i = -1821290720}) at kernel/qeventloop.cpp:200
#28 0x00007f358b1ff694 in QCoreApplication::exec () at kernel/qcoreapplication.cpp:880
#29 0x00007f357fdc863b in kdemain (argc=1, argv=0x70a350) at /build/buildd/kdebase-workspace-4.2.95/plasma/shells/desktop/main.cpp:50
#30 0x000000000040714e in launch (argc=1, _name=0x725128 "/usr/bin/plasma-desktop", args=<value optimized out>, cwd=0x0, envc=0, envs=0x725148 "", reset_env=false, tty=0x0, avoid_loops=false, 
    startup_id_str=0x40a309 "0") at /build/buildd/kde4libs-4.2.95/kinit/kinit.cpp:672
#31 0x0000000000407978 in handle_launcher_request (sock=7, who=<value optimized out>) at /build/buildd/kde4libs-4.2.95/kinit/kinit.cpp:1164
#32 0x0000000000407f25 in handle_requests (waitForPid=0) at /build/buildd/kde4libs-4.2.95/kinit/kinit.cpp:1357
#33 0x0000000000408a66 in main (argc=2, argv=0x7fff93715da8, envp=0x7fff93715dc0) at /build/buildd/kde4libs-4.2.95/kinit/kinit.cpp:1784

Thanks

this is a bug in a kubuntu patch:

http://bazaar.launchpad.net/%7Ekubuntu-members/kdebase-workspace/ubuntu/annotate/head%3A/debian/patches/kubuntu_71_default_plasma_layout.diff

if you don't have the folderview plugin (e.g. you haven't installed
kdebase-apps) it will crash. this is not in the upstream sources, however. i
just talked with Riddel about the issue on irc and gave him some tips on how to
improve the patch.

cheers, everyone.

*** Bug 200069 has been marked as a duplicate of this bug. ***