Updated Thunderbird on the laptop this morning to the new version 11.0 and noticed Lightning had stopped working. That is normal as whatever version of Lighting is installed only works with one version of Thunderbird. Looked in the add-ons manager and noticed there was an update of Lightning ready to go, just needed to restart Thunderbird for it to install. I tried to restart Thunderbird but noticed even though I had clicked the restart it was still running in the background. After killing the process and restarting Thunderbird it acted like Lightning was not even installed (no calendar options). I checked in Thunderbird add-ons manager and noticed Lightning was listed, but the 
icon was missing.
I ended up going to the Lightning page on AMO, downloading and reinstalling Lightning manually. Restarted Thunderbird and this time around everything worked. Not sure, if Lightning just didn’t upgrade properly or if because Thunderbird didn’t close down gracefully or if the two were related to each other. Nonetheless, if you are having trouble getting Lightning to update in Thunderbird 11 just go to the AMO page, download and manually update.
thanks, GURU, after some minutes of being shocked about not having my calendar any more – that helped me out immdiately! St
I’m trying to install lightning for the first time, but after finally getting it downloaded it tells me it’s not compatible with thunderbird 11. Any suggestions?
Each release of Lightning is tied to a specific version of Thunderbird. The version of Lightning you are trying to install will only work with Thunderbird 15/15.0.1. You will need to get an older version (1.3) which supports Thunderbird 11 or update to a more current version of Thunderbird.
thanks, i now have my calendar but can’t add a new event- it says there is a parsing error! What do I do now?
Not certain, sounds like a problem with Provider for Google Calendar add-on.
Thanks Guru, downloaded the google calendar add-on and all now working well 🙂
Thanks so much for posting this. I had the same issue and resolved it this way: went to the Add-Ons Manager in TBird and clicked on “Get Add-ons.” Lightning is one of the first that pops up. Clicked on that, clicked install, restarted, and good to go. Phew!
I am also having trouble getting Lightning to update in Thunderbird 11. I’ve downloaded the most recent version of Lightning as instructed above, but when I try to install it I get the message “Lightning could not be installed because it is not compatible with Firefox 11”
Any help would be appreciated. My calendar has disappeared and I’m lost without it!
Thanks,
Rita
Whoops, you can not install Lightning via Firefox. You need to download (right-click on link and select Save Link As) then either drag the XPI file into the Thunderbird add-ons manger or from within the Thunderbird add-ons manager click on the gear icon, select Install add-on from file… then locate in the dialog box where you downloaded Lightning and click OK. Once Lightning is installed, restart Thunderbird and your calendar(s) should be back and working.
Thanks, this did exactly the trick and eased my worries about not having calendar access!
Ok, I have been using lightning fine and had all my events in and today I opened it and my events had all disappeared! any suggestions?
We’re you launching Thunderbird or had your computer been hibernating/sleeping and when you resumed your events were missing? I’ve noticed since Thunderbird 14 or 15, it seems the Lightning add-on will ‘crash’ after a period of time. In that case, a simple restart of Thunderbird will fix this. If that does not work, just reinstall Lightning as it may have become damaged.
So how do I uninstall? It’s not an option in my downloads. I’m only on Thunderbird 11 so is that just as likely to crash? Really would like my events back and rapidly losing faith in lightning….