Try yum from the terminal first. I had to import the gpg keys for the rpms on a recent install as well. That may be your issue as well, but I don't use the gui for updates any more.
yum on the terminal works fine. I just wanted the applet to show me if there were any updates, which it doesn't.
I have the "yum" service turned on too so the automatic updates get done; it's a cosmetic issue really, though I can't get the applet GUI to fire up at all, even starting it directly from the command line.
I have the GPG keys installed already because autorpm requires them too.
Paul.
