Version:           4.1.2 (using KDE 4.1.2)
OS:                Linux
Installed from:    Ubuntu Packages

Here's the backtrace

mash@zeb:~$ dolphin
ASSERT: "(*it).isValid()" in file /build/buildd/kde4libs-4.1.2/kio/kio/previewjob.cpp, line 565
<unknown program name>(12485)/: Communication problem with  "dolphin" , it probably crashed.
Error message was:  "org.freedesktop.DBus.Error.NoReply" : " "Message did not receive a reply (timeout by message bus)" "

-----------------------------------------------
Application: Dolphin (dolphin), signal SIGABRT
(no debugging symbols found)
(no debugging symbols found)
(no debugging symbols found)
[Thread debugging using libthread_db enabled]
[New Thread 0xb5fc2970 (LWP 12486)]
[KCrash handler]
#6  0xb7fca410 in __kernel_vsyscall ()
#7  0xb6802085 in raise () from /lib/tls/i686/cmov/libc.so.6
#8  0xb6803a01 in abort () from /lib/tls/i686/cmov/libc.so.6
#9  0xb7608367 in qt_message_output (msgType=QtFatalMsg, 
    buf=0xbfe075ec "ASSERT: \"(*it).isValid()\" in file /build/buildd/kde4libs-4.1.2/kio/kio/previewjob.cpp, line 565") at global/qglobal.cpp:2061
#10 0xb7608458 in qFatal (msg=0xb774f498 "ASSERT: \"%s\" in file %s, line %d")
    at global/qglobal.cpp:2263
#11 0xb7608505 in qt_assert (assertion=0xb7f11146 "(*it).isValid()", 
    file=0xb7f11188 "/build/buildd/kde4libs-4.1.2/kio/kio/previewjob.cpp", 
    line=565) at global/qglobal.cpp:1831
#12 0xb7e4b321 in KIO::filePreview (items=@0xbfe096dc, width=160, height=128, 
    iconSize=0, iconAlpha=0, scale=true, save=false, enabledPlugins=0x0)
    at /build/buildd/kde4libs-4.1.2/kio/kio/previewjob.cpp:565
#13 0x0807e124 in ?? ()
#14 0xb6cd18b0 in QWidget::event (this=0x8296d90, event=0xbfe09b30)
    at kernel/qwidget.cpp:7216
#15 0xb6c79f9c in QApplicationPrivate::notify_helper (this=0x80b8ed8, 
    receiver=0x8296d90, e=0xbfe09b30) at kernel/qapplication.cpp:3800
#16 0xb6c7ece8 in QApplication::notify (this=0xbfe0b06c, receiver=0x8296d90, 
    e=0xbfe09b30) at kernel/qapplication.cpp:3765
#17 0xb7b9d483 in KApplication::notify (this=0xbfe0b06c, receiver=0x8296d90, 
    event=0xbfe09b30)
    at /build/buildd/kde4libs-4.1.2/kdeui/kernel/kapplication.cpp:311
#18 0xb76fc0b9 in QCoreApplication::notifyInternal (this=0xbfe0b06c, 
    receiver=0x8296d90, event=0xbfe09b30) at kernel/qcoreapplication.cpp:591
#19 0xb6ccfc3b in QWidgetPrivate::show_helper (this=0x8297840)
    at ../../include/QtCore/../../src/corelib/kernel/qcoreapplication.h:215
#20 0xb6ccf921 in QWidgetPrivate::show_recursive (this=0x8297840)
    at kernel/qwidget.cpp:6103
#21 0xb6ccfa8b in QWidgetPrivate::showChildren (this=0x8296a50, 
    spontaneous=false) at kernel/qwidget.cpp:6522
#22 0xb6ccfb51 in QWidgetPrivate::show_helper (this=0x8296a50)
    at kernel/qwidget.cpp:6179
#23 0xb6cd01b8 in QWidget::setVisible (this=0x82963f0, visible=true)
    at kernel/qwidget.cpp:6442
#24 0xb6ffeeb9 in QDockAreaLayoutInfo::restoreState (this=0x814d138, 
    stream=@0xbfe09e28, widgets=@0xbfe09da8, testing=false)
    at widgets/qdockarealayout.cpp:1939
#25 0xb6fff3aa in QDockAreaLayout::restoreState (this=0x814d0bc, 
    stream=@0xbfe09e28, _dockwidgets=@0xbfe09eac, 
    testing=<value optimized out>) at widgets/qdockarealayout.cpp:2223
#26 0xb702d4dd in QMainWindowLayoutState::restoreState (this=0x814d010, 
    _stream=@0xbfe09f54, oldState=@0x814d208)
    at widgets/qmainwindowlayout.cpp:687
#27 0xb702dd09 in QMainWindowLayout::restoreState (this=0x814d000, 
    stream=@0xbfe09f54) at widgets/qmainwindowlayout.cpp:2133
#28 0xb7028d04 in QMainWindow::restoreState (this=0x812cf80, 
    state=@0xbfe0a00c, version=0) at widgets/qmainwindow.cpp:1080
#29 0xb7c55822 in KMainWindow::applyMainWindowSettings (this=0x812cf80, 
    cg=@0x812cfdc, force=false)
    at /build/buildd/kde4libs-4.1.2/kdeui/widgets/kmainwindow.cpp:756
#30 0xb7c91012 in KXmlGuiWindow::applyMainWindowSettings (this=0x812cf80, 
    config=@0x812cfdc, force=<value optimized out>)
    at /build/buildd/kde4libs-4.1.2/kdeui/xmlgui/kxmlguiwindow.cpp:346
#31 0xb7c52e75 in KMainWindow::setAutoSaveSettings (this=0x812cf80, 
    group=@0xbfe0a0e0, saveWindowSize=true)
    at /build/buildd/kde4libs-4.1.2/kdeui/widgets/kmainwindow.cpp:957
#32 0xb7c52eec in KMainWindow::setAutoSaveSettings (this=0x812cf80, 
    groupName=@0xbfe0a124, saveWindowSize=<value optimized out>)
    at /build/buildd/kde4libs-4.1.2/kdeui/widgets/kmainwindow.cpp:945
#33 0xb7c910eb in KXmlGuiWindow::finalizeGUI (this=0x812cf80)
    at /build/buildd/kde4libs-4.1.2/kdeui/xmlgui/kxmlguiwindow.cpp:325
#34 0xb7c8f396 in KXMLGUIBuilder::finalizeGUI (this=0x812cf98)
    at /build/buildd/kde4libs-4.1.2/kdeui/xmlgui/kxmlguibuilder.cpp:409
#35 0xb7c90fc7 in KXmlGuiWindow::finalizeGUI (this=0x812cf80, 
    client=0x812cfc8)
    at /build/buildd/kde4libs-4.1.2/kdeui/xmlgui/kxmlguiwindow.cpp:355
#36 0xb7c9aef7 in KXMLGUIFactory::addClient (this=0x825cb50, client=0x812cfc8)
    at /build/buildd/kde4libs-4.1.2/kdeui/xmlgui/kxmlguifactory.cpp:269
#37 0xb7c91839 in KXmlGuiWindow::createGUI (this=0x812cf80, 
    xmlfile=@0xbfe0a3a0)
    at /build/buildd/kde4libs-4.1.2/kdeui/xmlgui/kxmlguiwindow.cpp:249
#38 0xb7c91a09 in KXmlGuiWindow::setupGUI (this=0x812cf80, 
    defaultSize=@0xbfe0a330, options=@0xbfe0a338, xmlfile=@0xbfe0a3a0)
    at /build/buildd/kde4libs-4.1.2/kdeui/xmlgui/kxmlguiwindow.cpp:207
#39 0xb7c91b11 in KXmlGuiWindow::setupGUI (this=0x812cf80, 
    options=@0xbfe0a3a4, xmlfile=@0xbfe0a3a0)
    at /build/buildd/kde4libs-4.1.2/kdeui/xmlgui/kxmlguiwindow.cpp:182
#40 0x0806c6c9 in _start ()
#0  0xb7fca410 in __kernel_vsyscall ()