I posted this question on the Mozilla forum several days ago, but no responses thus far. I figure the LQ experts might have a solutions ...

I recently updated to Thunderbird 115.6.0 on Linux. After doing so I can no longer add events to my calendar. In the error console I get the message, "An error occurred when writing to the calendar ... Could not find definition for Eastern Standard Time". This seems like a rather odd error. How do I fix it?

Or maybe find error msg reporting in https://archive.mozilla.org/pub/thun...15.6.0/source/ (nGB!)

I found the problem. I was also getting a MODIFICATION error from Thunderbird Calendar. The problem was that when I upgraded from Slackware 14.2 to 15.0 the Radicale CalDAV server was not compatible with the new Perl version. I discovered this by first trying to telnet to 5232 and got connection refused. I then did a 'ps ax' to see if radicale was running. It was not. Trying to start it showed the Perl error in syslog. I then downloaded and built a new radicale from SlackBuilds, made a couple of custom tweaks to the startup script and the config, and voila! Back in action!