After putting on my fresh Ubuntu Jaunty installation, my favourite Email client Thunderbird, the Lightning extension (version 0.9), didn't worked at all.
I tried everything, reinstalling Thunderbird several times, disabling all other extensions, nothing.
Lightning painted some icons, but that was everything.
Some incompatibility. I installed SunBird 0.9, and it works fine. Earlier Lightning versions seemed to work also, so what is the matter?
Finally, I found the solution in some forum, you need to have libstdc++ version 5 on your system (Jaunty comes with version 6 by default). And it has to be there, when Lightning extension 0.9 is installed, so if you already have it in your Thunderbird setup, uninstall it first, then put libstc++5 on your system, and reinstall the Lightning extension.
sudo aptitude install libstdc++5
# or if you don't want to install more stuff:
ln -s /usr/lib/libstdc++.so.6 /usr/lib/libstdc++.so.5