The activity manager cannot be terminated. I use an add-on to manage Google Calendar (https://addons.thunderbird.net/cs/thunderbird/addon/provider-for-google-calendar/). Today when I started Thunderbird there was an error when I logged this add-on into my Google account. So I temporarily cancelled the add-on , but in the activity manager I still see 4 activities called "Calendar Sync...." that I can't cancel. The activity manager is still running, no new messages are being received. I tried uninstalling and reinstalling the latest and current version, nothing helped. Current version of Thunderbird: 91.5.0 (64 bits) Windows CS Thanks for your help. MD