Thunderbird Lightning: cannot add new calendar
If the calendar plugin Thunderbird Lightning stops working after a system upgrade (Ubuntu 8.04 -> 9.10 in my case), just reinstall the libstdc++5 library. Before installing the library you have to deinstall the plugin from thunderbird and reinstall it afterwards.
The Thunderbird behaviour is a bit curious: the calendar and todo tabs are shown, but all previously defined calendars are missing. In addition it is not possible to add new calendars, these options are greyed out.