CalEvent popup triggers "This item has changed... server"

For discussing the Mozilla Calendar, Sunbird and Lightning projects.
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Joined: May 5th, 2016, 6:54 pm

Post Posted May 5th, 2016, 7:14 pm

Thunderbird ver 45.0, Lightning ver 4.7 syncing to DAV calendar at

In Lightning, a calendar event's popup reminder results in the dialog box "This item has recently been changed on the server. Submitting your changes will overwrite the changes made on the server:
<submit changes anyway> <discard my change/reload>

Regardless which I select, the box immediately reappears.

First: What is the implication of the message in that dialog box? I presume "server" means the calendar as it exists as a DAV service on my email provider's website. If there had not been a recent calendar edition/deletion/edit, why would there be "recent activity" on the server? I don't understand what I ought to infer from that message. And, it doesn't seem to matter which button I select; the dialog box immediately reappears.

The only way I've found to dismiss the original event pop-up reminder is to edit the event to delete it.

Also, I presume that is a feature, because if it were a bug, I have to believe something this annoying would by now have been fixed. I see this behavior has been documented as far back as 2010.

I'm charged with making a recommendation on a Linux-based Personal Information Manager package. Several features of Thunderbird + Lightning are desirable. The one we select will be used on about 80 Linux desktops. But the described behavior would be a support nightmare for me.

Does anyone monitor this forum who understands to working of the calendar event pop-up. Please?

Posts: 748
Joined: February 12th, 2005, 8:33 pm

Post Posted May 14th, 2016, 7:51 pm

As the dialog box doesn't work as it should, I think there is a problem with the DAV implementation at Or maybe there is a setting to change in your calendar preferences.

I have two calendars set up on our company's server (CalDAV) and two other one on Google calendar.
So here is what happens when the calendar works properly.

The message "This item has recently been changed on the server. Submitting your changes will overwrite the changes made on the server:
<submit changes anyway> <discard my change/reload>"
typically appears in three situations:
– I very recently created an event (less than 15 minutes ago), then reopen it to change a detail (ex.: location, add participant, set an alarm);
– There has just been an alarm which I have reset. Even though it's not a change per se, (The server considers it as if the server info has been updated; yet the only update is that the alarm is off.)
– I have very recently created an event or changed some details on another system (ex.: on my phone), and then I open the event on my computer.

In the first two cases, in spite of the warning, I know that what I have on my computer is up to date, so I clik on "submit changes anyway". In the last case, the server information is actually more accurate, so I press "discard my changes/reload". But in all these situations, I only see the warning ONCE, and it works as planned.

Now that I think of it, I never tried to update a repetitive event. Would it display the warning once for each occurrence of the event? But for single-occurrence events, it definitely works as planned.

– Thunderbird 45.1 on Windows 7 (French), using the built-in Lightning and the Provider for Google Calendars extension; 2 Google calendars and 2 on the office server (CalDAV; no other details on the server are known)

As I don't know if your problem lies with, some options you might have set up, or the Linux implementation of Thunderbird/Lightning, I would suggest you try to configure a Google calendar. As Google Calendar works correctly on Thunderbird for Windows, if you have a problem, then it's likely to be a problem with Thunderbird for Linux; but if you don't, then it's a problem with
Michel Gagnon
Montréal (Québec, Canada)

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Joined: June 19th, 2015, 4:52 am

Post Posted December 13th, 2016, 12:54 pm

Hi all - I know your conversation about this was several months ago, but I just wanted to add that I have this problem too, and I am using Google Calendar through Lightning using Google Provider. So it may have not been a problem with kirbo719's account. There could have been something else going on. I don't have a solution at the moment; would love to hear your thoughts and/or solutions that may have worked for you.

Things I have tried:
-uninstall T-bird
-uninstall Lightning
-restart apps and restart computer


Posts: 1
Joined: February 2nd, 2017, 12:08 am

Post Posted February 2nd, 2017, 12:35 am

I also have the Lightning calendar synched to my Google account calendar. The popup "This item has recenlty been changed on the server..." appears whether I have changed an event in the calendar in thunderbird or not and independently of whether I have changed an event in the Google calendar using my phone or not. After starting up Thunderbird, it appears almost straight away totally independently of whether i have changed anything on the Google calendar. It does not identify which event , if any, that it refers to. I have seem references to deleting an event to make it disappear, but as it is appearing independently of whether I have made changes at the google calendar/provider end or at the Lightning end, I am at a loss to know which event I should be deleting. A similar message does not appear when I have made changes to the calendar on my desktop in Lightning and these get synced with my phone without any problem. I have to select the "Submit my changes anyway " button about 10-20 times to clear it ( similarly if I select the "Discard my changes and reload" button. I have not made any changes to either calendar when this occurs.

I am getting close to considering abandoning using Lightning and or Thunderbird on my desktop as this is frankly annoying the crap out of me. I am unable to find any settings which will disable this popup from appearing. I understand the need for a warning if an event has been changed on both ends of the sync but this is happening when this is not the case. :( :( :( :(

Posts: 19
Joined: March 30th, 2007, 10:21 am

Post Posted February 16th, 2020, 6:11 pm

I, too, am getting this error message for a couple or few Calendar Events each time I launch Thunderbird, even though I have made no changes on Thunderbird, nor anywhere else, to these Events.

This has happened every now and then, pretty rarely, over the years and different versions of TB, but ever since I updated TB a few days ago to version 68.5.0, it happens each time I launch TB. Each time, it is about Events that it has not been about previously.

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