Could it be that some files were corupted, since I shut down the system "prematurely"?
Here is some backtrace...
Application: KOrganizer (korganizer), signal: Segmentation fault
[KCrash Handler]
#6 0xb6a163e7 in ?? () from /usr/lib/libQtGui.so.4
#7 0xb6a16553 in QSortFilterProxyModel::mapToSource(QModelIndex const&) const () from /usr/lib/libQtGui.so.4
#8 0xb6a16657 in ?? () from /usr/lib/libQtGui.so.4
#9 0xb6a17b71 in ?? () from /usr/lib/libQtGui.so.4
#10 0xb6a189f4 in QSortFilterProxyModel::qt_metacall(QMetaObject::Call, int, void**) () from /usr/lib/libQtGui.so.4
#11 0xb70d1b5a in ?? () from /usr/lib/libkorganizerprivate.so.4
#12 0xb61737aa in QMetaObject::metacall(QObject*, QMetaObject::Call, int, void**) () from /usr/lib/libQtCore.so.4
#13 0xb61821bb in QMetaObject::activate(QObject*, QMetaObject const*, int, void**) () from /usr/lib/libQtCore.so.4
#14 0xb61d3b59 in QAbstractItemModel::dataChanged(QModelIndex const&, QModelIndex const&) () from /usr/lib/libQtCore.so.4
#15 0xb70cca9d in ?? () from /usr/lib/libkorganizerprivate.so.4
#16 0xb70d4390 in ?? () from /usr/lib/libkorganizerprivate.so.4
#17 0xb70f483e in CalendarView::updateView(QDate const&, QDate const&, bool) () from /usr/lib/libkorganizerprivate.so.4
#18 0xb70f60f4 in CalendarView::updateView() () from /usr/lib/libkorganizerprivate.so.4
#19 0x080508eb in _start ()