Mervyn, the libstdc++5 package is no longer available in Karmic, so you need to remove the Lightning extension from inside Thunderbird (Tools->Addons), then install the lightning-extension package from the Universe repository. Your calendars and tasks from before the upgrade should still be available after this.
Mervyn, the libstdc++5 package is no longer available in Karmic, so you need to remove the Lightning extension from inside Thunderbird (Tools->Addons), then install the lightning-extension package from the Universe repository. Your calendars and tasks from before the upgrade should still be available after this.