I like the update-manager using Debian. This is default in any *buntu install, so you probably have no problem with this.
My problem occurred last night when I tried to launch the update-manager. True enough, the gksudo app was loaded, but nothing happened. I was asked to type in my password again, and again….
gksu and gksudo needs to look at the same /etc/sudoers as sudo does – you need to initialize gksu to do so. Run
and choose Authentication mode: sudo.
Save, and your gksudo should work.