The TV Forecast dashboard widget occasionally gets into a state where it becomes impossible to add new TV shows to the forecast. I’ve found that this usually happens immediately after an update. It is caused by the TV Forecast plist file somehow becoming corrupt. This is the file that contains the TV Forecast preferences.

The simplest fix to this problem is to delete the plist and start fresh. This file can be found at:

~/Library/Preferences/widget-com.mattcomi.widget.tvforecast.plist

The ~ denotes your user area.