Mozilla Thunderbird is currently at 38.5.0 Mozilla Firefox is currently at 43.0.4

It's possible that you have Thunderbird 43 but that would be a pre-release test version and not recommended for routine use.

Can you please recheck your version numbers, then someone can assist you with finding the correct version of Lightning.

In any case, a probable fix is to remove Lightning then download the current version and reinstall it. You won't have to do any setting up since the settings are left unchanged.

Your on a testing build... so a recommend you get onto the release channel. so download copy from getthunderbird.com and installing it. It will do the downgrade for you.

If you still have calendar issues, which may be probable as add-ons are designed to upgrade to newer versions and the downgrade may well not occur with the install as it is an older version.

1. On the toolbar then 
2. Select extensions and remove the Lightning (calendar) addon
3. Restart Thunderbird
4. Reinstall Lightning/calendar addon

My Thunderbird has just updated to 38.5.1 (release channel).

However (for both this update and the previous update) my add-on Lightning was ALSO updated to v4.5.0.1

This version of Lightning does NOT work! When I check the add-ons site, Lightning is still at v4.0.4.1 which does work. I do uninstall the "bad" addon and install the "good" one, but why is a Thunderbird update messing up the Lightning add-on?

If you have been using a prerelease version then you need to do some extra work to get it all back in sync. You are not on a pathway that a regular mainstream user would experience.

I recently beta tested 38.5.1 and it upgraded perfectly from 38.5.0. Generally speaking, it won't "downgrade" existing addons; it assumes you know what you are doing and you chose to go with a non-standard configuration. How else could developers test upcoming versions of their addons?

I really have no idea why I included all those instructions about what to do with lightning in my last posting to this thread. Instead of doing it your here asking how to do it. Please read and follow the instructions you were given. I even numbered them so you would not get the steps out of order..

Thank you for the responses but, unfortunately, I think you misunderstood my post.

I do not have a non-standard configuration.

I was on Thunderbird 38.5.0 which is the release version. I was and am using Lightning 4.0.4.1 also the release version (according to add-ons page).

When Thunderbird auto-updated to 38.5.1, the Lightning add-on was also updated in the same process (i.e. not by me) to v4.0.5.1 (additionally the same problem occurred previously when Thunderbird auto-updated to v38.5.0 so this was not a one-off occurrence).

This v4.0.5.1 version of Lightning does not work!

I have already uninstalled v4.0.5.1 and reinstalled Lightning v4.0.4.1. I was not asking how to do that!

My question was:

"Why is the Thunderbird auto-update process also updating the Lightning add-on to a version which is NOT available on the add-ons page?"

I do not have a non-standard configuration.

Why does the Mozilla 43.0 disable my Lightning Calendar?

Zenos said Ahem.Why does the Mozilla 43.0 disable my Lightning Calendar?

Sorry I am not the original poster and am not using Mozilla 43.0 - I just have a similar problem, admittedly not exactly the same.

TbGbe said

I was on Thunderbird 38.5.0 which is the release version. I was and am using Lightning 4.0.4.1 also the release version (according to add-ons page).

Perhaps you are actually suggesting that I should have created a new question rather than tag mine onto this one?

My excuse would be that this "Forum" is rather confusing when first using it. I found a question which (sort of) matched my problem as each Thunderbird update is disabling my Lightning add-on. If this is the case, then all I can do is apologize for any confusion caused by my actions.

My bad for assuming you were the OP. I should have read back before answering.

I don't know how to replicate your situation. As I mentioned previously I beta tested both TB38.5.0 and TB38.5.1 and both updated seamlessly, including correct versions of Lightning.

We still don't know what the OP meant by "Mozilla 43.0".

No problem Zenos

Thanks for replying at least :)

In my case both updates to TB38.5.0 and TB38.5.1 caused the problem. The first I put down to a "glitch" but after the second I wondered if this had been encountered before (and supplementary where Lightning v4.0.5.1 was coming from).

If relevant, I am on Windows 10 64bit

Zenos said

We still don't know what the OP meant by "Mozilla 43.0".

Newer Thunderbird users, especially if they do not use Firefox tend to sometimes say Mozilla and version instead of Mozilla Thunderbird or rather Thunderbird and version.

That some folk are still having issues on update is not denied. There is still an issue. The cause if the issue after the event is also well understood. What no one at this time understands is what causes this in the update process for a very small percentage of users.

What happens with and update is now lightning is bundled it is updated as well, to prevent a double download of lightning it has a version number o.o.1 highter that the version on AMO. It is however exactly the same build, just the version number is fudged to prevent a scond update.

When it goes wrong some how an old version of one of the files appears, even though the new version is installed.

To try and get a handle in this, are any of those affected people using a windows network and roaming profiles?

Is your user account on the machine stored anywhere but the default C: drive. For that matter is your Thunderbird profile anywhere but the default appdata location on the C: drive. (if you have no idea what I am talking about the answer is no. They do not set themselves up in a non standard way.)

What anti virus are you using? Another variable that might affect the file locking of files being updated.

Matt said

That some folk are still having issues on update is not denied. There is still an issue. The cause if the issue after the event is also well understood. What no one at this time understands is what causes this in the update process for a very small percentage of users. What happens with and update is now lightning is bundled it is updated as well, to prevent a double download of lightning it has a version number o.o.1 highter that the version on AMO. It is however exactly the same build, just the version number is fudged to prevent a scond update. When it goes wrong some how an old version of one of the files appears, even though the new version is installed.

Good to know I'm not alone then :)

To try and get a handle in this, are any of those affected people using a windows network and roaming profiles?

Nope - Standalone on Win 10 64bit

Is your user account on the machine stored anywhere but the default C: drive. For that matter is your Thunderbird profile anywhere but the default appdata location on the C: drive. (if you have no idea what I am talking about the answer is no. They do not set themselves up in a non standard way.)

Thunderbird is installed on D: drive, I do have Windows settings to put User info on D: but even so Thunderbird profile is on C: (in users/..../appdata/local )

What anti virus are you using? Another variable that might affect the file locking of files being updated.

Bitdefender Internet security 2016 (registered).