My fault: it's not a duplicate of bug 46245.
It's quite difficult to find a duplicate of it.
May help...:

From main.log:
2007-10-21 21:40:11,707 ERROR failed to mark 'ubuntu-desktop' for install (E:Unable to correct problems, you have held broken packages.)
2007-10-21 21:46:15,562 ERROR Dist-upgrade failed: 'Can't upgrade required meta-packages'

From apt.log:
ERROR:root:Unauthenticated packages found: 'afio apache2 apache2-mpm-prefork app-install-data app-install-data-commercial apport apport-gtk bind9-host capplets-data curl dbus dbus-1-utils democracyplayer democracyplayer-data dnsutils edgy-community-wallpapers evolution-data-server evolution-data-server-common festival ffmpeg file firefox firefox-gnome-support flashplugin-nonfree gawk gimp gimp-data gimp-python gnome-app-install gnome-btdownload gnome-control-center gnome-media gnome-media-common gnome-panel gnome-panel-data gstreamer0.10-ffmpeg gstreamer0.10-gl gstreamer0.10-pitfdll gstreamer0.10-plugins-bad-multiverse gstreamer0.10-plugins-farsight gstreamer0.10-plugins-ugly gstreamer0.10-plugins-ugly-multiverse gtkhtml3.8 hal hal-device-manager hal-info hwdb-client-common hwdb-client-gnome iptables lame language-pack-en language-pack-gnome-en lftp liba52-0.7.4 libapache2-mod-auth-mysql libartsc0 libavcodec0d libavformat0d libbind9-0 libboost-program-options1.33.1 libboost-python1.33.1 libboost-regex1.33.1 libboost-signals1.33.1 libboost-thread1.33.1 libbtctl4 libcamel1.2-10 libcurl3 libcurl3-gnutls libdbd-mysql-perl libdbi-perl libdbus-1-3 libdc1394-13 libdns22 libdvdnav4 libdvdread3 libebook1.2-9 libecal1.2-7 libedata-book1.2-2 libedata-cal1.2-6 libedataserver1.2-9 libedataserverui1.2-8 libegroupwise1.2-13 libestools1.2 libexchange-storage1.2-3 libexif12 libfreebob0 libfreetype6 libggi2 libgii1 libgii1-target-x libgimp2.0 libgl1-mesa-dri libgl1-mesa-glx libglib1.2 libglide2 libglu1-mesa libgnome-media0 libgnome-window-settings1 libgnomebt0 libgtkhtml3.8-15 libhal-storage1 libhal1 libisc11 libisccc0 libisccfg1 libiso9660-4 libjack0.100.0-0 libkrb53 liblame0 liblwres9 libmagic1 libmagick9 libmetacity0 libmjpegtools0c2a libmodplug0c2 libmono-data-tds1.0-cil libmono-security1.0-cil libmono-sharpzip0.84-cil libmono-sqlite1.0-cil libmono-system-data1.0-cil libmono-system-web1.0-cil libmono1.0-cil libmpeg2-4 libmultisync-plugin-backup libmultisync-plugin-evolution libmyspell3c2 libnautilus-burn4 libnspr4 libnss3 liboggflac3 libopenobex1 libpanel-applet2-0 libpng12-0 libportaudio2 libpostproc0d libpq5 libpulse0 libqt3-mt libqt4-core libqt4-gui libquicktime0 librapi2 librapi2-tools libslab0 libsmbclient libstlport4.6c2 libsvga1 libsynce0 libvlc0 libwxbase2.6-0 libwxgtk2.6-0 libxine-extracodecs libxine-main1 libxine1 libxine1-ffmpeg libxmlsec1 libxmlsec1-nss libxmlsec1-openssl libxvidcore4 libzzip-0-12 linux-headers-2.6.20-16 linux-headers-2.6.20-16-generic linux-headers-generic linux-image-2.6.20-16-generic linux-image-generic mesa-utils metacity metacity-common mindi mindi-busybox mjpegtools mondo mozilla-mplayer mozilla-plugin-vlc mpg123-alsa mplayer multisync mysql-client-5.0 mysql-server-5.0 nautilus-cd-burner openoffice.org openoffice.org-base openoffice.org-calc openoffice.org-common openoffice.org-core openoffice.org-draw openoffice.org-evolution openoffice.org-filter-mobiledev openoffice.org-gnome openoffice.org-gtk openoffice.org-impress openoffice.org-java-common openoffice.org-math openoffice.org-style-human openoffice.org-writer opera python python-apport python-gdbm python-launchpad-bugs python-minimal python-problem-report python-uno python2.4 python2.4-minimal python2.5 python2.5-minimal quicktime-utils rdesktop samba-common smbclient sox tcl8.4 tcpdump ttf-opensymbol tzdata unattended-upgrades unrar update-manager update-manager-core vim-common vim-tiny vino vlc vlc-nox vlc-plugin-alsa vlc-plugin-arts vlc-plugin-esd vlc-plugin-ggi vlc-plugin-glide vlc-plugin-sdl vlc-plugin-svgalib vorbis-tools wengophone xchat xchat-common xkeyboard-config xscreensaver-data xscreensaver-gl'


Bug reported by Niels is not the same:

From apt.log:
Traceback (most recent call last):
  File "/usr/share/apport/package_hook", line 15, in <module>
    import apport, apport.fileutils
ImportError: No module named apport
Could not import module, is a package upgrade in progress? Error: No module named apport.ui

From main.log:
Several of: 
2007-12-27 16:24:57,627 ERROR got an error from dpkg for pkg: 'tasksel-data': 'dependency problems - leaving unconfigured
'

From term.log:
Traceback (most recent call last):
  File "logging/__init__.py", line 753, in emit
  File "logging/__init__.py", line 731, in flush
IOError: [Errno 9] Bad file descriptor
  File "/usr/share/apport/package_hook", line 15, in <module>
    import apport, apport.fileutils
ImportError: No module named apport

2007-12-27 16:31:13,413 ERROR SystemError from cache.commit(): installArchives() failed