Are you talking about the default 'Home' local Thunderbird calendar or one you hook up to like Google ?

do you use any addons to link to calendar like Provider for Google ? If this is a gmail/google calendar then make sure you are using the up to date addon: https://addons.thunderbird.net/en-GB/thunderbird/addon/provider-for-google-calendar/

Yes, I am talking about the default 'home' local Thunderbird calendar that I have used successfully for years. I only have the 'Home ' calendar. I always keep Thunderbird updated. I have checked that the calendar has not been accidentally hidden. I have looked through my list of programs and cannot find anything called Google Provider. When I follow the link that you have provided a screen pops up asking how I want to open the file and I have no idea so it doesn't open or install. I have attached a 2 jpgs showing screen grabs. The first with 3 events added and then after closing and reopening Thunderbird a screen grabs with the events missing.

Hello there Kathy.cw We have read your message. We try to help you.

https://www.thunderbird.net/en-US/calendar/

https://addons.thunderbird.net/nl/thunderbird/addon/provider-for-google-calendar/?src=ss

It s more like we recommend yo to unregister everything of your current version. And take a fresh reinstall of one of the version s. We have sended you. Probably this issue disappears.

So do not send us a message again after trying.

http://kb.mozillazine.org/Calendars_-_Thunderbird

Greetings Firefox volunteer.

The link I provided was only for people trying to link up to their google calendar - but as you are only using the Home calendar, that link is of no use to you, so I'm not sure what День сумо was trying to resolve - maybe they misunderstood something. You certainly do not need any addons of any kind.

The update to 91* involved a major change. Please read release notes: https://www.thunderbird.net/en-US/thunderbird/91.0/releasenotes/

You say " I always keep Thunderbird updated.", so did you manually uninstall 78.13.0 and then download and install version 91.0.3 from the official website ? OR did you allow some updater software on your computer to update Thunderbird ?

Please note: Thunderbird version 78.12.0 would get updated to 78.13.0 if Thunderbird was in control of the update, because at this point Thunderbird is not auto updating to version 91*. So if it auto updated then you have another program on your computer controlling all the various updates for all the various programs on your computer. I would advise you let Thunderbird be solely in control of updates as updater software will not know that just because a new major release is available it does not mean people on previous versions will get an immediate auto update to that new major release - as per Release notes.

Regarding the Home calendar.....as it is non functioning, delete that calendar then create a new 'Home' calendar and make sure it is enabled. Do the events etc remain retained properly in the new home calendar?

Thankyou for your very helpful and detailed suggestions. I have tried the simple one first and created a new calendar then deleted the old one. I then closed and reopened Thunderbird and the test events I created were still there. So far so good. Next step is to try a restart. Occasionally I cannot open Thunderbird either from the task bar or the start button. I have no idea why and suspect some quirk of my old laptop. The way I fix that is to redownload Thunderbird directly from the Thunderbird site so I suspect I did download 91 although I don't remember the exact date and have my suspicions that the calendar problems occurred after that. Periodically I open Thunderbird and it tells me an upgrade is being installed. That happens automatically and I have always assumed that was triggered by Thunderbird and not some 3rd party software. Thanks again. Will leave this open until I am sure that it is fixed.

Can you check this for me. Menu app icon > Tools > Developer Tools > click on 'Error console'

Make the window as large as possible so as much info is displayed as possible. take a screenshot, save as jpeg image. Repeat the process if you cannot display it all in one go. Post the jpeg images in this forum question. The information may contain something useful for the developers.

OK - see attached

Just done a restart and the new calendar survived. So looks like that simple fix has solved it. Thanks. Also a Thunderbird update has just installed. It was installed by Thunderbird Update Installer. The calendar seems to have survived that too.

Cathycw

Be shure about that antivirus program. Keep your pc protected.

Greetings Thunderbird volunteer