I had the same problem. It looks I was able to fix this using the steps below:
1. Make sure you have a current backup, such as a Time Machine backup!
2. Go into Dashboard and close the World Clock widget(s).
3. Start the Finder app.
Select from the menu Go -> Go to Folder _or_ press SHIFT + COMMAND + G keys and enter
~/Library/Preferences then press the Go button.
There you should see the file widget-com.apple.widget.worldclock.plist and maybe also widget-com.apple.widget.worldclock.plist.lockfile
Delete them
4. Open Terminal and type the following command (case-sensitive): killall Dock
See if that works