You have been used to doing `foo', but now when you invoke it (or click the toolbar button or select the menu item), nothing (or an error) happens. The simplest explanation is that you are missing a package that is essential to you. You can either track it down and install it (there is a list of packages and brief descriptions of their contents in etc/PACKAGES), or install the `Sumo Tarball' (see Q2.0.14).