Didnt know where to post this,.. Only posting to get the solution out there. Scoured the net and only found part answers or out-dated documentation.
If you would like to use Zimbra CalDAV with Thunderbird's Lightning plugin, here is how you do it.
Also, This will be of great interest of anyone getting DAV_NOT_DAV or READ_FAILED messages in the error console.
I am using ZIMBRA. I would like to use CalDAV with Thunderbird Lightning. I can reach the CalDAV url through Firefox. But, Thunderbird Lightning error console complains that DAV_NOT_DAV - this collection is not available or not a dav collection.
Go to the password manager in Thunderbird and delete all entries. Then go to Lightning and delete all calendars. Shutdown Thunderbird.
Start Thunderbird. Create a new calendar, choose CalDav, use
Accept, give new name. Accept. Your next screen will be an authentication prompt. This will be the only username and password that Lightning will ever use, as default, for Calendar Authentication... So choose wisely.
To further explain:: That means that you can only use one user account to view calendars. So if you have a gmail account with calendars and a work account using Zimbra... you will only be able to authenticate to, and use, one of them.
Read the next post for a possible workaround for that. However, even if the workaround works for you, your username and password are saved in plaintext. And sent in plaintext. So be careful!
Contact Mozilla if you have any complaints about that.