Having upgraded to 2.12 from 2.0?? I find that sidebar widgets are not working and are not available from admin. The plugin is installed and was working. As sidebar widgets is the most useful thing ever I am keen to get it back. They are listed as compatible with 2.12 so I can only think the default (kubrick) theme is the problem.
As I remember, the theme was modified for sidebar widgets.
Where do I go from here please?