To all who may be using this configuration (and possibly Sunbird on it's own too)
I had been using this configuration for some time running up against both 6.0.2 FOSS and 6.0.3 FOSS editions with no problems.
I upgraded to 6.0.4 and a couple of days later noticed my calerndars were no longer connecting. The GUI was showing the small warning triangle icon next to the calendar names, and the Thunderbird Error Console was listing an error message in the following format ...
Warning: There has been an error reading data for calendar: Work. However, this error is believed to be minor, so the program will attempt to continue. Error code: DAV_NOT_DAV. Description: The resource at http://<server>/dav/<user>/Work is either not a DAV collection or not available
I tried deleting & recreating the calendar reference multiple times to no avail. It was driving me nuts!
As I had recently upgraded the Lightening plug-in to the official 1.0 Beta 1 I suspected they broke something. So, I rolled back to the old version - still nothing worked. I could not roll back Zimbra 6.0.4 just for my issue so thought I was done for.
Eventually I ran Wireshark on my connection as I started Thunderbird - And VOILA !
91 26.300014 192.168.200.167 192.168.200.9 HTTP/XML PROPFIND /dav/<User>/Calendar/ HTTP/1.1
92 26.302353 192.168.200.167 192.168.200.9 HTTP/XML PROPFIND /dav/<User>/Tasks/ HTTP/1.1
93 26.314123 192.168.200.9 192.168.200.167 HTTP HTTP/1.1 401 invalid username/password
94 26.315490 192.168.200.9 192.168.200.167 HTTP HTTP/1.1 401 invalid username/password
Thunderbird was never asking for a password but yet was failing to authenticate as though I had typed one in. There could only be one reason ...
Password Manager !
I opened up Options --> Security --> Passwords --> Saved Passwords
and clicked on the Show Passwords button.
There I could immediately see the source of my problems. The saved password for
under my username was out of date. Now it all made sense, as I had just last week changed my network password.
I highlighted the line, and deleted it.
As soon as I restarted Thunderbird, it prompted me for my username and password for the Calendar connection, and once again offered to store it in Password Manager.
Calendar appointment reminders popped for the meetings I had "missed" over the past few days, and everything is once again working beautifully.
So, bottom line ... In my case at least the Password Manager was the root of the issue. It seems that somehow the Mozilla team has forgotten to prompt for updated userid/password in Lightening after an authentication failure.
For reference I just checked and found a Mozilla Bug has been opened for this issue
If you have a bugzilla login, please go over and vote for this to be fixed.
Note: I also use the Zindus extension - and it prompts me to update the out of date password whenever it fails to connect.
I hope this helps some others avoid the hassles I have had.
And, until they address the issue, remember .... If you change your Zimbra password - immediately go into Password Manager and delete the Zimbra entries