which lightning do you use?

On the current Thunderbird the lightning seems to get updated and since then it doe not work.
In the list with the extensions, the Lightning is included, but the icon is missing.
No signs of any lightning otherwise.
This was the lightning 2.6.1

I tried then to install the previous version 2.6, but also this one does not seem to work, the calendar tab is empty, it seems not to be able to read the calendar file properly.

Anybody with some experience on this?