Thanks for your help everyone - very much appreciated.
I am pleased to confirm that after starting in safe mode, uninstalling (not just disabling) Lightning, and then installing Iceowl, my email and calendar are working again.
Thanks for your help everyone - very much appreciated.
I am pleased to confirm that after starting in safe mode, uninstalling (not just disabling) Lightning, and then installing Iceowl, my email and calendar are working again.