rendering fails

Any idea why rendering is failing on my project?

All profiles end up with 0% and a waiting status forever and I see nothing interesting in the debug output.

Using debian-multimedia.org based packaging for kdenlive 0.7.3-0.0svn3376 and:

Versions of packages kdenlive depends on:
ii kdebase-runtime 4:4.2.2-1 runtime components from the offici
ii kdelibs5 4:4.2.2-2 core libraries for all KDE 4 appli
ii libc6 2.9-12 GNU C Library: Shared libraries
ii libgcc1 1:4.4.0-4 GCC support library
ii libmlt++1 1:0.3.8-0.0svn1428 An open source multimedia framewor
ii libmlt1 1:0.3.8-0.0svn1428 An open source multimedia framewor
ii libqt4-dbus 4.5.1-2 Qt 4 D-Bus module
ii libqt4-network 4.5.1-2 Qt 4 network module
ii libqt4-svg 4.5.1-2 Qt 4 SVG module
ii libqt4-xml 4.5.1-2 Qt 4 XML module
ii libqtcore4 4.5.1-2 Qt 4 core module
ii libqtgui4 4.5.1-2 Qt 4 GUI module
ii libsdl1.2debian 1.2.13-4+b1 Simple DirectMedia Layer
ii libstdc++6 4.4.0-4 The GNU Standard C++ Library v3
ii mlt 1:0.3.8-0.0svn1428 An open source multimedia framewor

Versions of packages kdenlive recommends:
ii dvgrab 3.2-2+b1 grab digital video data via IEEE13
pn frei0r (no description available)
ii swh-plugins 0.4.15-1 Steve Harris's LADSPA plugins

Versions of packages mlt depends on:
ii ffmpeg 5:0.5+svn20090508-0.0 audio/video encoder, streaming ser
ii libc6 2.9-12 GNU C Library: Shared libraries
ii libmlt1 1:0.3.8-0.0svn1428 An open source multimedia framewor

Versions of packages ffmpeg depends on:
ii libavcodec52 5:0.5+svn20090508-0.0 library to encode decode multimedi
ii libavdevice52 5:0.5+svn20090508-0.0 ffmpeg device handling library
ii libavfilter0 5:0.5+svn20090508-0.0 a graphics library;
ii libavformat52 5:0.5+svn20090508-0.0 ffmpeg file format library
ii libavutil50 5:0.5+svn20090508-0.0 avutil shared libraries
ii libc6 2.9-12 GNU C Library: Shared libraries