wassung,

Does your issue reproduce if you start Thunderbird in safe mode? https://support.mozilla.org/en-US/kb/safe-mode-thunderbird

And what addons do you have installed?

I have this issue too, it is fixed by opening in safe mode. I have narrowed down the bug to the popular add on 'thunderbird conversations'. By disabling this alone the problem is gone, only issue is I really don't like using thunderbird without this extension! I'd really like to roll-back until this issue is fixed

Ok, so I've fixed the issue. I just needed to manually update the 'thunderbird conversations' add on, then restart thunderbird. It works again now.

By opening in 'safe' mode, emails old and new can be opened BUT there is no Lightning nor the facility to open Google calendar!!!!!!! Have tried installing Lightning but no joy

does it just sit there telling you to restart Thunderbird to complete the installation?

a message "loading" appears beneath the list of e-mails but nothing further happens. the problem appears to be the Lightning add on. starting tbird using safe mode enables the normal email function but neither Lightning nor Google calendar operate

Just try reinstalling from GetThunderbird.com. There are issues with lightning and the update. I don't follow exactly what, but a reinstall usually fixes it.

Thank you to the community (Wayne, mdangelo32) for your help.........Matt's suggestion works!!!