If it doesn't show up in the plugin options, then it means it's not installed. Try to reinstall the plugin. It could be also possible that with the Ubuntu upgrade, the folder that rhythmbox searches for its plugins has changed.
Post output of this command: "locate rhythmbox | grep plugins"
If it doesn't show up in the plugin options, then it means it's not installed. Try to reinstall the plugin. It could be also possible that with the Ubuntu upgrade, the folder that rhythmbox searches for its plugins has changed.
Post output of this command: "locate rhythmbox | grep plugins"