If you upgrade to a new Thunderbird version you may have problems with the calendar data if you go back to an older version since historically Lightning versions have been closely tied to specific Thunderbird releases. It was originally going to be integrated with Thunderbird 3.0 but wasn't ready in time. I'd also recommend taking a look at the Calendar:GDATA Provider wiki page which covers installation/setup of the provider.Lightning is the most well known, provides the most functionality and gets the most attention/support from Mozilla Messaging. So, if you're getting errors updating your Google Calendar using CalDAV, you might try the Provider for Google Calendar to see if it fixes your issues.

After changing all my calendars to use the new provider, everything seems to be working very well. This got me to look into if there were other solutions other than CalDAV and I came across Provider for Google Calendar 0.7.1 add-on for Sunbird and Lightning.

The one thing that did keep popping up is that Google considers CalDAV support still experimental, so problems may occur.

After doing some searching, I found lots of threads of people having the same issue, but alas no solutions. Today I had several GoToMeeting invites that I need to add to my calendar and decided look into the problem again. While this works, it's no where near as fast as accepting an invite from Thunderbird. I ended up resorting to opening up Google Calendar and adding the events via the web interface. I could view events just fine and even dismiss alarms, but nothing I tried would allow me to add new events directly from Thunderbird. When ever I'd try to update an event, I'd get a very generic 'MODIFICATION_FAILED' error message with no detailed message. For a while now I've been dealing with issues adding/updating events to my Google Calendar from Thunderbird/Lightning.

Thunderbird google calendar