In version 1.0.1 and earlier, choosing "File > Edit list.." worked only from the menu screen.
You can see which version of Sona Vocabulary Assistant you have by looking at the bottom right of the menu screen. You can also check for updates by choosing "Help > Check for updates..."
If you can't get an updated version for some reason, a workaround for versions 1.01 and earlier is to be sure to return to the Menu screen before choosing "File > Edit list.."