I found that when the pages had no subpages, and the widget was in a sidebar/topbar or whereever by itself, the bar would appear and it would be empty. I'm not sure, I don't think it's an issue with the plugin, maybe... So I have added options to have alternative text display when there are no subpages.
Again, this is only an issue when the subpages are displayed in a sidebar with no other widgets and the sidebar is formatted differently to the rest of the page. Because I can't get in touch with the author I have also hosted this externally.
It can be found here: http://wordpress.dav3.net/subpages.zip