All my Tasks are gone too. Great.

Try this:

• Menu app icon > Help > More Troubleshooting Information
• Under 'Application Basics' - half way down - Profile Folder - Click on 'Open folder'

A new window opens showing the contents of your 'profile name' folder.

• Exit Thunderbird if running....this is important

• Click on 'calendar-data' folder to see contents.

You should see a 'backup' folder and some files.

• In calendar-data folder - Rename 'local.sqlite' to 'local.sqlite.bak'

• Click on 'backup' folder to see contents.

You should see file: 'local.v22.sqlite' of good size. Let me know if you other files as there may have been more than one backup.

• Copy the 'local.v22.sqlite' file and paste it into the 'calendar-data' folder (same place as the 'local.sqlite.bak')
• Rename 'local.v22.sqlite' as 'local.sqlite'

Start Thunderbird.

check calendar events and tasks.