Remove the associated preference file for World Clock to resolve this issue.
- 

- From the Finder, hold down the Option key and select Go > Library. 

- Open the Preferences folder in the window that appears. 

- Locate the widget-com.apple.widget.worldclock.plist file in the Preferences folder. Drag this item to the Trash. 

- Log out of your account, then log back in. 

- Open Dashboard. 

- Click the settings button (i) on the World Clock widget. 

- Re-add your world clock locations.